ITEM 1.    BUSINESS

GENERAL

We are a corporation incorporated under the laws of the state of Oklahoma, and our common stock is listed on the NYSE under the trading symbol “OKE.” We are the sole general partner and, as of December 31, 2015 , owned 41.2 percent of ONEOK Partners (NYSE: OKS), one of the largest publicly traded master limited partnerships. Our goal is to provide management and resources to ONEOK Partners, enabling it to execute its growth strategies and allowing us to grow our dividend. ONEOK Partners applies its core capabilities of gathering, processing, fractionating, transporting, storing and marketing natural gas and NGLs through the rebundling of services across the value chains through vertical integration in an effort to provide its customers with premium services at lower costs. ONEOK Partners is a leader in the gathering, processing, storage and transportation of natural gas in the United States. In addition, ONEOK Partners owns one of the nation’s premier natural gas liquids systems, connecting NGL supply in the Mid-Continent, Permian and Rocky Mountain regions with key market centers.

Separation of Natural Gas Distribution Business - In January 2014, we completed the separation of our former natural gas distribution business into a stand-alone publicly traded company, ONE Gas (NYSE: OGS). ONEOK shareholders of record at the close of business on January 21, 2014, retained their current shares of ONEOK stock and received one share of ONE Gas stock for every four shares of ONEOK stock owned in a transaction that was tax-free to ONEOK and its shareholders. In connection with the separation, we received a cash payment of approximately $1.13 billion from ONE Gas and utilized the proceeds to repay outstanding commercial paper and approximately $550 million of long-term debt.

Wind Down of Energy Services - We completed the wind down of our former energy services business on March 31, 2014. See additional discussion in Note B to the Consolidated Financial Statements included in this Annual Report.

EXECUTIVE SUMMARY

Commodity Price Environment - Due in part to the rapid growth in crude oil and natural gas production in the United States, the global supply of crude oil and natural gas exceeded demand and led to a dramatic fall in commodity prices beginning in the fourth quarter 2014. Lower crude oil and natural gas prices persisted throughout 2015 and are expected to remain low in 2016. The production growth and decline in crude oil prices have also contributed to lower NGL product prices, as well as narrow NGL product price differentials.

WTI crude oil prices declined to an average of approximately $50.00 per barrel in 2015, compared with prices averaging approximately $93.00 per barrel in 2014. NYMEX natural gas prices also declined to an average of approximately $2.60 per MMBtu in 2015, compared with prices averaging approximately $4.30 per MMBtu in 2014. OPIS Conway propane prices averaged less than $0.41 per gallon in 2015, compared with prices averaging more than $1.10 per gallon in 2014. At December 31, 2015, prices for WTI crude oil, NYMEX natural gas and OPIS Conway propane declined to approximately $35.00 per barrel, $2.30 per MMBtu and $0.33 per gallon, respectively, and remained weak into early 2016.

ONEOK Partners has mitigated partially its exposure to the current commodity price environment by growing its fee-based business. ONEOK Partners has a predominantly fee-based business in the Natural Gas Liquids and Natural Gas Pipelines segments and, historically to a lesser extent, in the Natural Gas Gathering and Processing segment. In 2015, however, the Natural Gas Gathering and Processing segment restructured many POP with fee contracts associated with a significant amount of its gathered volumes to increase the fee-based component and will continue to seek opportunities to similarly restructure additional contracts in 2016. These restructured contracts favorably impacted ONEOK Partners’ 2015 results, and it expects to receive the full benefit of the improved earnings from these contracts in its 2016 financial results. In the fourth quarter 2015, the Natural Gas Gathering and Processing segment’s fee revenues averaged $0.55 per MMBtu, compared with an average of $0.36 per MMBtu in 2014. As a result of these restructured contracts, we expect the Natural Gas Gathering and Processing segment’s fee-based earnings to increase significantly to more than 75 percent in 2016 and ONEOK Partners’ consolidated fee-based earnings to increase to approximately 85 percent in 2016. To further mitigate the impact of lower commodity prices, ONEOK Partners has hedged a significant portion of the Natural Gas Gathering and Processing segment’s expected equity volumes for 2016 and 2017. The Natural Gas Liquids and Natural Gas Pipelines segments continue to provide primarily fee-based services, and many of the contracts in these segments include fixed fee, minimum volume or firm demand charge agreements that provide a minimum level of revenues regardless of commodity prices or volumetric throughput.

The current weakened commodity price environment, resulting from factors beyond our control, is creating challenges for ONEOK Partners’ crude oil and natural gas producer customers and resulted in decreased drilling activity in 2015, compared

with 2014. In the Williston Basin, the number of rigs drilling on acreage dedicated to ONEOK Partners decreased from approximately 80 rigs in January 2015 to approximately 30 rigs in December 2015. Despite the sustained lower crude oil, natural gas and NGL prices and reduced capital spending by producers, we continue to expect demand for midstream services and infrastructure development to be driven by producers who need to connect production with end-use markets where current infrastructure is insufficient or nonexistent. ONEOK Partners’ natural gas and NGL volumes increased in 2015, particularly in the Williston Basin, as producers are focusing their drilling in the most productive areas and are using more efficient drilling and completion techniques. We expect this lower commodity price environment to continue in 2016, which will impact ONEOK Partners’ net realized prices for natural gas, NGLs and condensate, as well as our financial results. If the low commodity price environment persists for a prolonged period or prices decline further, volumes across ONEOK Partners’ assets may grow more slowly than in the past or decline.

In the future, we expect commodity prices to recover; however, the timing of this recovery is uncertain. We do not expect commodity prices to return in the near term to the levels experienced in the first half of 2014.

Supply - Natural gas and NGL supply is affected by producer drilling activity, which is sensitive to commodity prices, operating capacity, access to capital and regulatory control. Crude oil and natural gas price declines have continued since 2014, which has resulted in fewer active drilling rigs within ONEOK Partners’ areas of operations. Although drilling has slowed, many of ONEOK Partners’ customers continue to drill new wells in the most productive areas, and improvements in drilling and completion technology are resulting in higher volumes from the wells that are completed. These new technologies, such as multi-well pads and more efficient drilling rigs, are resulting in lower drilling and completion costs, which are mitigating partially the lower commodity prices for ONEOK Partners’ producer customers. In addition, new wells drilled using horizontal drilling technologies tend to produce volumes at higher initial production rates resulting generally in higher initial decline rates than conventional vertical wells; however, the decline rates flatten out over time. A significant portion of ONEOK Partners’ Williston Basin gathering and processing assets are in the most productive areas, which typically produce at higher initial production rates compared with other areas, have the highest natural gas content and have slower natural gas declines than crude oil. We expect ONEOK Partners’ natural gas gathered and processed volumes in the Williston Basin to continue to grow in 2016, despite expected reductions in producer drilling activity. The significant drilling activity in recent years in the Williston Basin has caused natural gas production to exceed the capacity of existing natural gas gathering and processing infrastructure, which results in the flaring of natural gas (the controlled burning of natural gas at the wellhead) by producers. We expect ONEOK Partners to capture a substantial amount of natural gas currently being flared by producers due to an additional processing plant and compression projects that were placed in service in late 2015 and projects that are expected to be completed in 2016. Additionally, we expect ONEOK Partners to benefit from production from new wells on acreage dedicated to ONEOK Partners in the Williston Basin that have been drilled previously but have not yet been completed or connected to its system by expanding its natural gas gathering and processing and natural gas liquids gathering infrastructure in the Williston Basin.

Supply growth has resulted in available ethane supplies that are greater than the petrochemical industry’s current demand. As a result, low or unprofitable price differentials between ethane and natural gas have resulted in ethane rejection at most of ONEOK Partners’ and its customers’ natural gas processing plants connected to its natural gas liquids gathering system in the Mid-Continent and Rocky Mountain regions during 2014 and 2015, which reduced natural gas liquids volumes gathered, fractionated, transported and sold across our assets. Through ethane rejection, natural gas processors leave much of the ethane component in the natural gas stream sold at the tailgate of natural gas processing plants. We expect ethane rejection to persist at current levels, which have exceeded 150 MBbl/d on ONEOK Partners’ natural gas liquids system during 2015, until ethylene producers increase their capacity to consume additional ethane feedstock volumes through plant modifications, plant expansions and the completion of announced new world-scale ethylene production projects, which are anticipated to begin coming on line in 2017. Ethane rejection is expected to continue to have a significant impact on our and ONEOK Partners’ financial results into 2017.

Beginning in June 2015, the Natural Gas Gathering and Processing segment reduced its level of ethane rejection in the Williston Basin to alleviate downstream NGL product specification issues, which offsets partially the financial impact of ethane rejection. We expect this decreased ethane rejection to continue throughout 2016. In addition, the Natural Gas Liquids segment’s integrated assets enable ONEOK Partners to mitigate partially the impact of ethane rejection through minimum volume commitments, contract modifications that vary fees for ethane and other NGL products, and ONEOK Partners’ ability to utilize the transportation capacity made available due to ethane rejection to capture additional NGL location price differentials, when they exist, in its optimization activities. See additional discussion in the “Financial Results and Operating Information” section of Item 7, Management’s Discussion and Analysis of Financial Condition and Results of Operation.

Growth Projects - In 2015, crude oil and natural gas producers continued to drill for crude oil and NGL-rich natural gas in many regions where ONEOK Partners has operations, including in the Bakken Shale and Three Forks formations in the

Williston Basin; in the Cana-Woodford Shale, Woodford Shale, Springer Shale, Stack and SCOOP areas in the Mid-Continent region; and in the Permian Basin. In response to this continued production of crude oil, natural gas and NGLs, and higher demand for NGL products from the petrochemical industry, ONEOK Partners has completed growth projects and acquisitions in these regions. In addition, ONEOK Partners’ current projects are expected to expand its natural gas gathering and processing and natural gas liquids gathering infrastructure in the Williston Basin to capture natural gas currently being flared by producers. Through its Roadrunner joint venture, ONEOK Partners is constructing a pipeline to transport natural gas from the Permian Basin in West Texas to the Mexican border near El Paso, Texas. The Roadrunner pipeline will connect with ONEOK Partners’ existing natural gas pipeline and storage infrastructure in Texas and, together with ONEOK Partners’ ONEOK WesTex Transmission (WesTex) intrastate natural gas pipeline system expansion project, is expected to create a platform for future opportunities to deliver natural gas supply to Mexico. The execution of these capital investments aligns with ONEOK Partners’ strategy to generate consistent growth and sustainable earnings. ONEOK Partners’ contractual commitments from crude oil and natural gas producers, natural gas processors and electric generators are expected to provide incremental cash flows and long-term fee-based earnings.

While reduced crude oil and natural gas producer drilling activity is slowing supply growth, we expect ONEOK Partners to complete its previously announced projects to meet crude oil and natural gas producers’ demands for its gathering, processing, fractionation and transportation services. ONEOK Partners has suspended capital expenditures for certain natural gas processing plants and related infrastructure to align with the needs of its customers. ONEOK Partners could resume its suspended capital-growth projects when market conditions improve and customers’ needs change. In 2016, we expect lower capital spending for ONEOK Partners, compared with spending levels from 2013 through 2015, due to the current commodity price environment and ONEOK Partners’ alignment of capital-growth projects with the needs of its customers. If the current commodity price environment persists for a prolonged period, it may further impact the timing or demand for additional infrastructure projects or growth opportunities in the future.

Impairment Charges - In the fourth quarter 2015, ONEOK Partners recorded $264.3 million of noncash impairment charges, primarily related to its long-lived assets and equity investments in the dry natural gas area of the Powder River Basin.

Cash Dividends/Distributions - During 2015 , we paid cash dividends of $2.43 per share, an increase of approximately 14 percent from the $2.125 per share paid during 2014 . In January 2016 , we declared a dividend of $0.615 per share ( $2.46 per share on an annualized basis).

During 2015 , ONEOK Partners paid cash distributions to its limited partners of $3.16 per unit, an increase of approximately 5 percent over the the $3.01 per unit paid during 2014 . In January 2016 , ONEOK Partners GP declared a cash distribution to ONEOK Partners’ limited partners of $0.79 per unit ( $3.16 per unit on an annualized basis) for the fourth quarter 2015 .

Liquidity - Our primary sources of cash inflows are distributions to us from our general partner and limited partnership interests in ONEOK Partners. The cash distributions that we expect to receive from ONEOK Partners are expected to provide sufficient resources to finance our operations and quarterly cash dividends. As of December 31, 2015 , we had $92.5 million of cash on hand and access to our $300 million ONEOK Credit Agreement, which matures in January 2020. We do not expect any principal debt-service requirements until our next long-term debt maturity in 2022.

ONEOK Partners relies primarily on operating cash flows, commercial paper, bank credit facilities, debt issuances and the issuance of common units for its liquidity and capital resources requirements. As of December 31, 2015 , ONEOK Partners had $5.1 million of cash on hand and available capacity under its Partnership Credit Agreement of approximately $1.8 billion . In addition, in January 2016, ONEOK Partners entered into the $1.0 billion senior unsecured Term Loan Agreement with a syndicate of banks that matures in January 2019. Proceeds from the Term Loan Agreement effectively refinance ONEOK Partners’ 2016 debt maturities.

The significant decline in commodity prices has increased the cost of debt and equity financing for ONEOK Partners and others in the industry. While lower commodity prices and industry uncertainty may result in increased financing costs, we believe ONEOK Partners has secured sufficient access to the financial resources and liquidity necessary to meet its requirements for working capital, debt service payments and capital expenditures through 2016 and well into 2017.

See Item 7, Management’s Discussion and Analysis of Financial Condition and Results of Operation, for more information on our growth projects, results of operations, liquidity and capital resources.

BUSINESS STRATEGY

Our primary business strategy is to maximize dividend payout while maintaining prudent financial strength and flexibility, with a focus on safe, reliable, environmentally responsible and legally compliant operations for our customers, employees, contractors and the public through the following:

NARRATIVE DESCRIPTION OF BUSINESS

We report operations in the following business segments:

Natural Gas Gathering and Processing

Overview - The Natural Gas Gathering and Processing segment provides nondiscretionary services to contracted producers in North Dakota, Montana, Wyoming, Kansas and Oklahoma. It provides exploration and production companies with gathering and processing services that allow them to move their raw (unprocessed) natural gas to market. Raw natural gas is gathered, compressed and transported through pipelines to processing facilities. In order for the raw natural gas to be accepted by the downstream market, it must have contaminants, such as water, nitrogen and carbon dioxide, removed as well as NGLs separated for further processing. Processed natural gas, usually referred to as residue natural gas, is then recompressed and delivered to natural gas pipelines and end users. The separated NGLs are in a mixed, unfractionated form and are sold and delivered through natural gas liquids pipelines to fractionation facilities for further separation.

Rocky Mountain region - The Williston Basin is located in portions of North Dakota and Montana, including the oil-producing, NGL-rich Bakken Shale and Three Forks Formation, and is ONEOK Partners’ most active region with continued volume growth and additional gathering and processing infrastructure needs. ONEOK Partners’ growth projects are expected to increase its gathering and processing capacity and allow it to capture natural gas from new wells being drilled, wells that have been drilled but have not yet been completed, and natural gas currently being flared by producers. The significant Williston Basin drilling activity in recent years has caused natural gas production to exceed the capacity of existing natural gas gathering and processing infrastructure, which results in the flaring of natural gas by producers. See further discussion of growth projects in Item 7, Management’s Discussion and Analysis of Financial Condition and Results of Operations, including expected completion dates.

The Powder River Basin is located in Wyoming. This region includes the NGL-rich Frontier, Turner Sussex and Niobrara Shale where ONEOK Partners’ Sage Creek system provides gathering and processing services to customers in the southeast portion of Wyoming.

Mid-Continent region - ONEOK Partners’ Mid-Continent region is located in Western Oklahoma, which includes the NGL-rich Cana-Woodford Shale, Stack, SCOOP, Woodford Shale, Springer Shale and the Mississippian Lime Formation; and Southwest

Kansas, which includes the Hugoton Basin, Central Kansas Uplift Basin and the Mississippian Lime Formation. The Mid-Continent region includes active drilling in the Cana-Woodford Shale, Woodford Shale, Springer Shale, Stack and SCOOP areas in Oklahoma as well as mature areas with volumetric declines.

Revenues - Revenues for this segment are derived primarily from the following types of contracts:

Over time as ONEOK Partners’ contracts are renewed or restructured, it has generally increased the fee components and reduced the percent of proceeds retained from the sale of the commodities. As a result, ONEOK Partners’ mix of commodity and fee-based earnings continue to change as volumes naturally decline on older contracts where it retains a higher percent of proceeds and volumes increase on contracts with higher fee components. Additionally, under certain POP with fee contracts ONEOK Partners’ fee revenues may increase or decrease if production volumes, delivery pressures or commodity prices change relative to specified thresholds.

ONEOK Partners’ gathering and processing agreements have terms ranging from month to month to life of lease. Generally, its gathering and processing agreements are long-term agreements, typically five to 10 years. ONEOK Partners has restructured many of its contracts to significantly increase its fee-based earnings and will continue to seek opportunities to similarly restructure additional contracts in 2016. As a result of these restructured contracts, we expect the Natural Gas Gathering and Processing segment’s fee-based earnings to increase significantly and to favorably impact ONEOK Partners’ 2016 results. In the fourth quarter 2015, the Natural Gas Gathering and Processing segment’s fee rates averaged $0.55 per MMBtu, compared with an average of $0.36 per MMBtu in 2014. ONEOK Partners’ NGLs, natural gas and crude oil commodity price sensitivity in this segment is expected to decrease in 2016 as a result of these restructured contracts. Additionally, ONEOK Partners uses commodity derivative instruments and physical-forward contracts to reduce its near-term sensitivity to fluctuations in the natural gas, crude oil and NGL prices received for its share of volumes under POP with fee contracts.

Unconsolidated Affiliates - The Natural Gas Gathering and Processing segment includes the following unconsolidated affiliates:

See Note P of the Notes to Consolidated Financial Statements in this Annual Report for additional discussion of our unconsolidated affiliates.

Market Conditions and Seasonality - Supply - Rocky Mountain region - In the Williston Basin, natural gas volumes continued to grow in 2015 as new well connections to ONEOK Partners’ system from drilling completions increased, driven primarily by producer development of Bakken Shale crude oil wells, which also produce associated natural gas containing significant quantities of NGLs. We expect a reduction in well connections in 2016, compared with 2015, due to continued low commodity prices and reduced drilling and completion activity. Volumes are expected to increase in the Williston Basin due to the following:

The NGL-rich natural gas from the Niobrara area in the Powder River Basin has experienced a reduction in drilling activity due to the current price environment; however, ONEOK Partners’ long-term volume expectations have not materially changed due to the quality of reserves in these proven formations.

Mid-Continent region - In the Mid-Continent region, ONEOK Partners has significant natural gas gathering and processing assets in Oklahoma and Kansas. We expect ONEOK Partners’ average natural gas gathered volumes to grow in 2016 due to continued drilling and completion activity in the Cana-Woodford Shale, Woodford Shale, Springer Shale, Stack and SCOOP areas in Oklahoma, offset partially by the natural volume declines from existing wells that supply ONEOK Partners’ natural gas gathering and processing facilities. Producers in the region are targeting their projects by drilling in the most productive areas and minimizing their costs by taking advantage of efficient drilling and completion techniques.

If the commodity price environment remains low or declines further, volumes in each region may grow more slowly than in the past or decline.

See further discussion of supply in the “Executive Summary” section.

Demand - Demand for gathering and processing services is dependent on production by producers, which is driven by the strength of the economy; natural gas, crude oil and NGL prices; and the demand for each of these products from end users. The Natural Gas Gathering and Processing segment’s customers are generally crude oil and natural gas producers who have proven reserves or are currently producing gas in areas within ONEOK Partners’ existing infrastructure. ONEOK Partners’ gathering and processing services are nondiscretionary for these producer customers, as the raw natural gas stream they produce has no marketable value until it is gathered and processed into commodities. Additionally, demand is impacted by the weather.

Rocky Mountain region - Demand for ONEOK Partners’ gathering and processing services in the Williston Basin has remained strong even as crude oil prices have declined. Requirements in North Dakota to reduce producer natural gas flaring have increased the need for ONEOK Partners’ services to capture this natural gas.

Mid-Continent region - Demand for ONEOK Partners’ service remained constant and is linked directly to proven production sources and drilling and completion activities, which are primarily in the Cana Woodford, Springer Shale, Stack and SCOOP areas in Oklahoma. If the commodity price environment remains low or declines further, demand for ONEOK Partners’ services in this region may grow more slowly than in the past or decline.

Commodity Prices - See discussion of commodity prices in the “Executive Summary” section.

Seasonality - Cold temperatures usually increase demand for natural gas, the main heating fuel for homes and businesses. Warm temperatures usually increase demand for natural gas used in gas-fired electric generators for residential and commercial cooling, as well as agriculture related equipment like irrigation pumps and crop dryers. During periods of peak demand for a certain commodity, prices for that product typically increase. However, in the current environment of natural gas oversupply and high storage levels, we do not expect prices to be materially affected by seasonality.

Extreme weather conditions can impact the volumes of natural gas gathered and processed. Freeze-offs are a phenomenon where water produced from natural gas freezes at the wellhead or within the gathering system. This causes a temporary

interruption in the flow of natural gas. All of ONEOK Partners’ operations may be affected by other weather conditions that may cause a loss of electricity at our facilities or prevent access to certain locations that affect a producer’s ability to complete wells or ONEOK Partners’ ability to connect those wells to its systems.

Competition - ONEOK Partners competes for natural gas supply with major integrated oil companies, independent exploration and production companies that have gathering and processing assets, pipeline companies and their affiliated marketing companies, and other midstream gatherers and processors. The factors that typically affect ONEOK Partners’ ability to compete for natural gas supply are:

Competition for natural gas gathering and processing services continues to increase as new infrastructure projects are completed to address increased production from shale and other resource areas. In response to these changing industry conditions, ONEOK Partners continues to evaluate opportunities to increase earnings and cash flows, and reduce risk by:

Customers - ONEOK Partners’ Natural Gas Gathering and Processing segment provides nondiscretionary services to crude oil and natural gas producers that include the gathering and processing of natural gas produced from crude oil and natural gas wells. ONEOK Partners’ customers include both large integrated and independent exploration and production companies. ONEOK Partners is not typically exposed to material credit risk with producer customers under POP with fee contracts as it receives proceeds from the sale of commodities and remits a portion of those proceeds back to the crude oil and natural gas producers. In 2015, 99 percent of the downstream commodity sales in the Natural Gas Gathering and Processing segment were made to investment-grade customers, as rated by S&P or Moody’s, or our comparable internal ratings, or secured by letters of credit or other collateral.

Government Regulation - The FERC traditionally has maintained that a natural gas processing plant is not a facility for the transportation or sale of natural gas in interstate commerce and, therefore, is not subject to jurisdiction under the Natural Gas Act. Although the FERC has made no specific declaration as to the jurisdictional status of ONEOK Partners’ natural gas processing operations or facilities, its natural gas processing plants are primarily involved in extracting NGLs and, therefore, are exempt from FERC jurisdiction. The Natural Gas Act also exempts natural gas gathering facilities from the jurisdiction of the FERC. We believe ONEOK Partners’ natural gas gathering facilities and operations meet the criteria used by the FERC for nonjurisdictional natural gas gathering facility status. Interstate transmission facilities remain subject to FERC jurisdiction. The FERC has historically distinguished between these two types of facilities, either interstate or intrastate, on a fact-specific basis. ONEOK Partners transports residue natural gas from its natural gas processing plants to interstate pipelines in accordance with Section 311(a) of the Natural Gas Policy Act. Oklahoma, Kansas, Wyoming, Montana and North Dakota also have statutes regulating, to varying degrees, the gathering of natural gas in those states. In each state, regulation is applied on a case-by-case basis if a complaint is filed against the gatherer with the appropriate state regulatory agency.

Rocky Mountain region - In July 2014, the North Dakota Industrial Commission (NDIC) approved a policy designed to limit natural gas flaring at existing and future crude oil wells in the Williston Basin. The policy establishes crude oil production limits that will take effect if a producer fails to meet requirements to capture natural gas at the wellhead. ONEOK Partners continues to participate actively on the North Dakota Petroleum Council’s Flaring Task Force, which provides recommendations to the NDIC on policies and targets. In 2015, the NDIC passed updated natural gas capture percentages and associated timelines. None of these changes are expected to have a material impact on available production. ONEOK Partners is constructing additional natural gas gathering pipelines, processing plants and natural gas liquids pipeline capacity that are expected to help alleviate capacity constraints. As a result, we expect ONEOK Partners’ natural gas gathered and processed volumes in the Williston Basin to continue to grow in 2016, despite expected reductions in producer drilling activity, as

ONEOK Partners captures natural gas currently being flared by producers and natural gas produced with new drilling focused in the most productive areas.

See further discussion in the “Regulatory, Environmental and Safety Matters” section.

Natural Gas Liquids

Overview - The Natural Gas Liquids segment owns and operates facilities that gather, fractionate, treat and distribute NGLs and store NGL products, primarily in Oklahoma, Kansas, Texas, New Mexico and the Rocky Mountain region where it provides nondiscretionary services to producers of NGLs and delivers those products to the two primary market centers, one in the Mid-Continent in Conway, Kansas, and the other in the Gulf Coast in Mont Belvieu, Texas. It owns or has an ownership interest in FERC-regulated natural gas liquids gathering and distribution pipelines in Oklahoma, Kansas, Texas, New Mexico, Montana, North Dakota, Wyoming and Colorado, and terminal and storage facilities in Missouri, Nebraska, Iowa and Illinois. ONEOK Partners also owns FERC-regulated natural gas liquids distribution and refined petroleum products pipelines in Kansas, Missouri, Nebraska, Iowa, Illinois and Indiana that connect its Mid-Continent assets with Midwest markets, including Chicago, Illinois. The majority of the pipeline-connected natural gas processing plants in Oklahoma, Kansas and the Texas Panhandle, which extract unfractionated NGLs from unprocessed natural gas, are connected to its gathering systems. ONEOK Partners owns and operates truck- and rail-loading and -unloading facilities connected to its natural gas liquids fractionation and pipeline assets. In November 2014, ONEOK Partners began transporting unfractionated NGLs from natural gas processing plants in the Permian Basin after completion of the West Texas LPG acquisition.

Most natural gas produced at the wellhead contains a mixture of NGL components, such as ethane, propane, iso-butane, normal butane and natural gasoline. The NGLs that are separated from the natural gas stream at the natural gas processing plants remain in a mixed, unfractionated form until they are gathered, primarily by pipeline, and delivered to fractionators where the NGLs are separated into NGL products. These NGL products are then stored or distributed to the Natural Gas Liquids segment’s customers, such as petrochemical manufacturers, heating fuel users, ethanol producers, refineries, exporters and propane distributors.

Revenues for the Natural Gas Liquids segment are derived primarily from nondiscretionary fee-based services that ONEOK Partners provides to its customers and from the physical optimization of its assets. The segment’s fee-based services have increased due primarily to new supply connections; expansion of existing connections; the completion of capital projects, including the Bakken NGL Pipeline and Sterling III Pipeline; the West Texas LPG acquisition; and expansion of its NGL fractionation capacity, including the completion of its MB-2 and MB-3 fractionators. The segment’s sources of earnings are categorized as exchange services, transportation and storage services, optimization and marketing and isomerization, which are defined as follows:

Excess NGL supply continues to result in narrow NGL location price differentials between the Mid-Continent and Gulf Coast market centers. We expect these narrow price differentials to persist as NGL production continues to increase and new fractionators and pipelines from various NGL-rich shale areas throughout the country, including ONEOK Partners’ growth projects, have alleviated historical constraints affecting NGL prices and location price differentials between the Conway, Kansas, and Mont Belvieu, Texas, market centers.

Unconsolidated Affiliates - The Natural Gas Liquids segment includes the following unconsolidated affiliates:

See Note P of the Notes to Consolidated Financial Statements in this Annual Report for additional discussion of unconsolidated affiliates.

Market Conditions and Seasonality - Supply - The unfractionated NGLs that ONEOK Partners gathers and transports originate primarily from natural gas processing plants connected to ONEOK Partners’ gathering systems in Oklahoma, Kansas, Texas, New Mexico and the Rocky Mountain region. ONEOK Partners’ fractionation operations receive NGLs from a variety of processors and pipelines, including its affiliates, located in these regions. Supply for the Natural Gas Liquids segment depends on crude oil and natural gas drilling and production activities by producers, the decline rate of existing production, natural gas processing plant economics and capabilities, and the NGL content of the natural gas that is produced and processed in the areas in which ONEOK Partners operates.

See additional discussion of supply in the “Executive Summary” section.

Demand - Demand for NGLs and the ability of natural gas processors to successfully and economically sustain their operations affect the volume of unfractionated NGLs produced by natural gas processing plants, thereby affecting the demand for NGL gathering, fractionation and distribution services. Natural gas and propane are subject to weather-related seasonal demand. Other NGL products are affected by economic conditions and the demand associated with the various industries that utilize the commodity, such as butanes and natural gasoline used by the refining industry as blending stocks for motor fuel, denaturant for ethanol and diluents for crude oil. Ethane, propane, normal butane and natural gasoline are used by the petrochemical industry to produce chemical products, such as plastic, rubber and synthetic fibers. Several petrochemical companies are constructing new plants, plant expansions, additions or enhancements that improve the light-NGL feed capability of their facilities due primarily to the increased supply and attractive price of ethane, compared with crude oil-based alternatives, as a petrochemical feedstock in the United States. The demand is expected to increase significantly beginning in 2017 when many of the new petrochemical plants and plant modifications are expected to be completed. We do not expect the recent decline in crude oil, natural gas and natural gas liquids prices to impact adversely the construction of new petrochemical plants or plant modifications in the Gulf Coast region. In addition, we expect increased international demand for ethane, propane and butane to provide opportunities to increase fee-based earnings in ONEOK Partners’ exchange and storage services and marketing activities.

Commodity Prices - The Natural Gas Liquids segment provides primarily fee-based services. However, ONEOK Partners is exposed to market risk associated with changes in the price of NGLs; the location differential between the Mid-Continent, Chicago, Illinois, and Gulf Coast regions; and the relative price differential between natural gas, NGLs and individual NGL products, which affect its NGL purchases and sales, and its exchange, storage, transportation, optimization and marketing financial results. Since 2013, supply growth from the development of NGL-rich areas and increased capacity available on pipelines that connect the Mid-Continent and Gulf Coast market centers resulted in NGL price differentials remaining narrow between the Mid-Continent market center at Conway, Kansas, and the Gulf Coast market center at Mont Belvieu, Texas. NGL storage revenue may be affected by price volatility and forward pricing of NGL physical contracts versus the price of NGLs on the spot market.

See additional discussion of commodity prices in the “Executive Summary” section.

Seasonality - ONEOK Partners’ natural gas liquids fractionation and pipeline operations typically experience some seasonal variation. Some NGL products stored and transported through its assets are subject to weather-related seasonal demand, such as propane, which can be used to heat homes during the winter heating season and for agricultural purposes such as crop drying in the fall. Demand for butanes and natural gasoline, which are primarily used by the refining industry as blending stocks for motor fuel, denaturant for ethanol and diluents for crude oil, may also be subject to some variability during seasonal periods when certain government restrictions on motor fuel blending products change. The ability of natural gas processors to produce NGLs also is affected by weather. Extreme weather conditions can impact the volumes of natural gas gathered and processed and NGL volumes gathered, transported and fractionated. Freeze-offs are a phenomenon where water produced from natural gas freezes at the wellhead or within the gathering system. This causes a temporary interruption in the flow of natural gas and,

consequently, NGLs. Conversely, in periods of hot weather, the natural gas processing plants become less efficient in NGL recovery, and thus NGL recovery during the summer typically decreases.

Competition - The Natural Gas Liquids segment competes with other fractionators; intrastate and interstate pipeline companies; storage providers and gatherers and transporters for NGL supply in the Rocky Mountain, Permian, Mid-Continent and Gulf Coast regions. The factors that typically affect ONEOK Partners’ ability to compete for NGL supply are:

ONEOK Partners has responded to these factors by making capital investments to access new supplies; increasing gathering, fractionation and distribution capacity; increasing storage, withdrawal and injection capabilities; and reducing operating costs so that it may compete effectively. ONEOK Partners’ competitors are constructing or have completed new natural gas liquids pipeline and fractionation projects to address the growing NGL supply and petrochemical demand. As ONEOK Partners’ growth projects and those of its competitors have alleviated constraints between the Mid-Continent and Gulf Coast NGL market centers, we expect the narrow location price differentials between the two locations to continue. In addition, new natural gas liquids pipeline projects constructed by third parties are expected to bring incremental NGL supply from the Rocky Mountain, Marcellus and Utica basins to the Gulf Coast market center that may affect NGL prices, as well as compete with or displace NGL supply volumes from the Mid-Continent and Rocky Mountain regions where ONEOK Partners’ assets are located. We believe ONEOK Partners’ natural gas liquids fractionation, pipelines and storage assets are located strategically, connecting diverse supply areas to market centers.

Customers - The Natural Gas Liquids segment’s customers are primarily NGL and natural gas gathering and processing companies; major and independent crude oil and natural gas production companies; propane distributors; ethanol producers; and petrochemical, refining and NGL marketing companies. ONEOK Partners earns fee revenue from NGL and natural gas gathering and processing customers and natural gas liquids pipeline transportation customers. ONEOK Partners is not typically exposed to material credit risk on the majority of its exchange services fee revenues, as ONEOK Partners purchases NGLs from its gathering and processing customers and deducts fees from the amounts it remits. This segment also earns commodity sales revenue on the downstream sales of NGL products. In 2015, more than 80 percent of this segment’s commodity sales were made to investment-grade customers, as rated by S&P or Moody’s, or our comparable internal ratings, or secured by letters of credit or other collateral. In addition, the majority of the Natural Gas Liquids segment’s pipeline tariffs provide ONEOK Partners the ability to require security from shippers.

Government Regulation - The operations and revenues of ONEOK Partners’ natural gas liquids pipelines are regulated by various state and federal government agencies. Its interstate natural gas liquids pipelines are regulated by the FERC, which has authority over the terms and conditions of service; rates, including depreciation and amortization policies; and initiation of service. In Oklahoma, Kansas and Texas, certain aspects of ONEOK Partners’ intrastate natural gas liquids pipelines that provide common carrier service are subject to the jurisdiction of the OCC, KCC and RRC, respectively.

PHMSA has asserted jurisdiction over certain portions of ONEOK Partners’ fractionation facilities in Bushton, Kansas, that it believes are subject to its jurisdiction. ONEOK Partners has objected to the scope of PHMSA’s jurisdiction and is seeking resolution of this matter. ONEOK Partners does not anticipate that the cost of compliance will have a material adverse effect on its consolidated results of operations, financial position or cash flows.

See further discussion in the “Regulatory, Environmental and Safety Matters” section.

Natural Gas Pipelines

Overview - The Natural Gas Pipelines segment provides transportation and storage services to end users through its wholly owned assets and its 50 percent ownership in Northern Border Pipeline. ONEOK Partners’ 50-50 Roadrunner joint venture currently is under construction, with Phase I expected to be completed in the first quarter 2016.

Interstate Pipelines - ONEOK Partners’ interstate pipelines are regulated by the FERC and are located in North Dakota, Minnesota, Wisconsin, Illinois, Indiana, Kentucky, Tennessee, Oklahoma, Texas and New Mexico. ONEOK Partners’ interstate pipeline companies include:

Intrastate Pipelines - ONEOK Partners’ intrastate natural gas pipeline assets in Oklahoma transport natural gas through the state and have access to the major natural gas producing formations, including the Cana-Woodford Shale, Woodford Shale, Springer Shale, Granite Wash, Stack, SCOOP and Mississippian Lime. ONEOK Partners’ intrastate natural gas pipeline assets in Oklahoma serve end-use markets, such as local distribution companies and power generation companies. In Texas, ONEOK Partners’ intrastate natural gas pipelines are connected to the major natural gas producing formations in the Texas Panhandle, including the Granite Wash formation and Delaware and Cline producing formations in the Permian Basin. The pipelines are capable of transporting natural gas throughout the western portion of Texas, including the Waha Hub where other pipelines may be accessed for transportation to western markets, exports to Mexico, the Houston Ship Channel market to the east and the Mid-Continent market to the north. ONEOK Partners also has access to the natural gas producing formations in south central Kansas. Through its Roadrunner joint venture, ONEOK Partners is constructing a pipeline to transport natural gas from the Permian Basin in West Texas to the Mexican border near El Paso, Texas. The Roadrunner pipeline will connect with ONEOK Partners’ existing natural gas pipeline and storage infrastructure in Texas and, together with its WesTex intrastate natural gas pipeline expansion project, is expected to create a platform for future opportunities to deliver natural gas supply to Mexico.

Transportation Rates - ONEOK Partners’ transportation contracts for its regulated natural gas activities are based upon rates stated in the respective tariffs. The tariffs provide both the general terms and conditions for the facilities and the maximum allowed rates customers can be charged by type of service, which may be discounted to meet competition if necessary. The rates are established at FERC or the appropriate state jurisdictional agencies. The revenues are primarily fee based from the following types of services:

Storage - ONEOK Partners owns natural gas storage facilities located in Texas and Oklahoma that are connected to its intrastate natural gas pipelines. It also has underground natural gas storage facilities in Kansas. In Texas and Kansas, natural gas storage operations may be regulated by the state in which the facility operates and by the FERC for certain types of services. In Oklahoma, natural gas storage operations are not subject to rate regulation by the state and have market-based rate authority from the FERC for certain types of services.

Storage Rates - The revenues are primarily fee based from the following types of services:

Unconsolidated Affiliates - The Natural Gas Pipelines segment includes the following unconsolidated affiliates:

See Note P of the Notes to Consolidated Financial Statements in this Annual Report for additional discussion of unconsolidated affiliates.

Market Conditions and Seasonality - Supply - The development of natural gas produced from shale resource areas has continued to increase available supply across North America and has caused location and seasonal price differentials to narrow in the regions where ONEOK Partners operates.

Interstate - Guardian Pipeline, Midwestern Gas Transmission and Viking Gas Transmission access supply from the major producing regions of the Mid-Continent, Rocky Mountains, Canada, Gulf Coast and the Northeast. The current supply of natural gas for Northern Border Pipeline is primarily sourced from Canada; however, as the Williston Basin supply area continues to develop, more natural gas supply from this area is expected to be transported on Northern Border Pipeline to markets near Chicago. In addition, supply volumes from nontraditional natural gas production areas, such as the Marcellus and Utica shale area in the Northeast, may compete with and displace volumes from the Mid-Continent, Rocky Mountain and Canadian supply sources in our markets. Factors that may impact the supply of Canadian natural gas transported by ONEOK Partners’ pipelines are primarily the availability of United States supply, Canadian natural gas available for export, Canadian storage capacity, government regulation and demand for Canadian natural gas in Canada and United States consumer markets.

Intrastate and Storage - ONEOK Partners’ intrastate pipelines and storage assets may be impacted by the pace of drilling activity by crude oil and natural gas producers and the decline rate of existing production in the major natural gas production areas in the Mid-Continent region, which includes the Cana-Woodford Shale, Granite Wash and Mississippian Lime areas, Hugoton Basin and Central Kansas Uplift Basin.

Demand - Demand for services is related directly to the segment’s access to supply and the demand for natural gas by the markets that its natural gas pipelines and storage facilities serve. Demand is also affected by weather, the economy, natural gas price volatility and regulatory changes.

Commodity Prices - As a result of excess supplies of natural gas and the addition of natural gas infrastructure, the natural gas location and seasonal price differentials have remained narrow across the regions where ONEOK Partners operates. Although ONEOK Partners’ revenues are primarily fee based, commodity prices can affect its results of operations.

Seasonality - Demand for natural gas is seasonal. Weather conditions throughout North America may significantly impact regional natural gas supply and demand. High temperatures may increase demand for gas-fired electric generation needed to meet the electricity demand required to cool residential and commercial properties. Cold temperatures may lead to greater demand for ONEOK Partners’ transportation services due to increased demand for natural gas to heat residential and commercial properties. Low precipitation levels may impact the demand for natural gas that is used to fuel irrigation activity in the Mid-Continent region.

To the extent that pipeline capacity is contracted under firm-service transportation agreements, revenue, which is generated primarily from fixed fee charges, is not significantly impacted by seasonal throughput variations. However, when transportation agreements expire, seasonal demand may affect the value of firm-service transportation capacity.

Natural gas storage is necessary to balance the relatively steady natural gas supply with the seasonal demand of residential, commercial and electric-generation users. The majority of ONEOK Partners’ storage capacity is contracted under firm-service agreements; however, it retains a portion of its storage capacity for operational purposes, and the remaining capacity is used to provide park-and-loan services.

Competition - This segment’s natural gas pipelines and storage facilities compete directly with other intrastate and interstate pipeline companies and other storage facilities. Competition among pipelines and natural gas storage facilities is based primarily on fees for services, quality and reliability of services provided, current and forward natural gas prices, proximity to natural gas supply areas and markets, and access to capital. Competition for natural gas transportation services continues to increase as new infrastructure projects are completed and the FERC and state regulatory bodies continue to encourage more competition in the natural gas markets. Regulatory bodies also are encouraging the use of natural gas for electric generation that has traditionally been fueled by coal. The cost of coal and the associated rail transportation continues to compete with natural gas for this market; however, the clean-burning aspects of natural gas and abundance of supply make it an economically competitive and environmentally advantaged alternative. We believe that ONEOK Partners’ pipelines and storage assets compete effectively due to their strategic locations connecting supply areas to market centers and other pipelines.

Customers - This segment’s natural gas pipeline assets primarily serve local natural gas distribution companies, electric-generation facilities, large industrial companies, municipalities, irrigation customers and marketing companies. Utility customers generally require ONEOK Partners’ services regardless of commodity prices. In 2015, more than 85 percent of the revenues in this segment were from investment-grade customers, as rated by S&P or Moody’s, or our comparable internal ratings, or secured by letters of credit or other collateral. In addition, the majority of the Natural Gas Pipeline segment’s pipeline tariffs provide ONEOK Partners the ability to require security from shippers.

Government Regulation - Interstate - ONEOK Partners’ interstate natural gas pipelines are regulated under the Natural Gas Act and Natural Gas Policy Act, which give the FERC jurisdiction to regulate virtually all aspects of this business, such as transportation of natural gas, rates and charges for services, construction of new facilities, depreciation and amortization policies, acquisition and disposition of facilities, and the initiation and discontinuation of services.

In November 2012, the FERC initiated a review of Viking Gas Transmission’s rates pursuant to Section 5 of the Natural Gas Act. The parties reached agreement on the terms of a settlement that provides for a 2 percent reduction in transportation rates. The settlement was approved by the FERC in December 2013, and the revised rates became effective January 1, 2014.

In August 2014, Viking Gas Transmission filed a prefiling “Stipulation and Agreement in Resolutions of All Issues Concerning Adjustment in Rates of Viking Gas Transmission Company” (settlement) with the FERC. The settlement was approved on October 1, 2014, and became final on October 31, 2014. Rates under the settlement became effective January 1, 2015.

Intrastate - ONEOK Partners’ intrastate natural gas pipelines in Oklahoma, Kansas and Texas are regulated by the OCC, KCC and RRC, respectively. While it has flexibility in establishing natural gas transportation rates with customers, there is a maximum rate that it can charge its customers in Oklahoma and Kansas. In Kansas and Texas, natural gas storage may be regulated by the state and by the FERC for certain types of services. In Oklahoma, natural gas storage is not subject to rate regulation by the state, and ONEOK Partners has market-based rate authority from the FERC for certain types of services.

See further discussion in the “Regulatory, Environmental and Safety Matters” section.

SEGMENT FINANCIAL INFORMATION

Operating Income, Customers and Total Assets - See Note S of the Notes to Consolidated Financial Statements in this Annual Report for disclosure by segment of our operating income and total assets and for a discussion of revenues from external customers.

Other

Through ONEOK Leasing Company, L.L.C. and ONEOK Parking Company, L.L.C., we own an office building (ONEOK Plaza) and a parking garage in downtown Tulsa, Oklahoma, where our headquarters are located. ONEOK Leasing Company, L.L.C. leases excess office space to others and operates our headquarters office building. ONEOK Parking Company, L.L.C. owns and operates a parking garage adjacent to our headquarters.

REGULATORY, ENVIRONMENTAL AND SAFETY MATTERS

Environmental Matters - ONEOK Partners is subject to multiple historical preservation, wildlife preservation and environmental laws and/or regulations that affect many aspects of its present and future operations. Regulated activities include, but are not limited to, those involving air emissions, storm water and wastewater discharges, handling and disposal of solid and hazardous wastes, wetlands preservation, hazardous materials transportation, and pipeline and facility construction. These laws and regulations require ONEOK Partners to obtain and/or comply with a wide variety of environmental clearances, registrations, licenses, permits and other approvals. Failure to comply with these laws, regulations, licenses and permits may expose ONEOK Partners to fines, penalties and/or interruptions in its operations that could be material to our results of operations. For example, if a leak or spill of hazardous substances or petroleum products occurs from pipelines or facilities that ONEOK Partners owns, operates or otherwise uses, ONEOK Partners could be held jointly and severally liable for all resulting liabilities, including response, investigation and cleanup costs, which could affect materially our results of operations and cash flows. In addition, emissions controls and/or other regulatory or permitting mandates under the Clean Air Act and other similar federal and state laws could require unexpected capital expenditures at ONEOK Partners’ facilities. We cannot assure that existing environmental statutes and regulations will not be revised or that new regulations will not be adopted or become applicable to ONEOK Partners.

In June 2013, the Executive Office of the President of the United States (the President) issued the President’s Climate Action Plan, which includes, among other things, plans for further regulatory actions to reduce carbon emissions from various sources. In March 2014, the President released the Climate Action Plan - Strategy to Reduce Methane Emissions (Methane Strategy) that lists a number of actions the federal agencies will undertake to continue to reduce above-ground methane emissions from several industries, including the oil and natural gas sectors. The proposed measures outlined in the Methane Strategy include, without limitation, the following: collaboration with the states to encourage emission reductions; standards to minimize natural gas venting and flaring on public lands; policy recommendations for reducing emissions from energy infrastructure to increase the performance of the nation’s energy transmission, storage and distribution systems; and continued efforts by PHMSA to require pipeline operators to take steps to eliminate leaks and prevent accidental methane releases and evaluate the progress of states in replacing cast-iron pipelines. The impact of any such regulatory actions on ONEOK Partners’ facilities and operations is unknown. ONEOK Partners continues to monitor these developments and the impact they may have on its businesses. Revised or additional statutes or regulations that result in increased compliance costs or additional operating restrictions could have a significant impact on our financial position, results of operations and cash flows.

Pipeline Safety - ONEOK Partners is subject to PHMSA regulations, including pipeline asset integrity-management regulations. The Pipeline Safety Improvement Act of 2002 requires pipeline companies operating high-pressure pipelines to perform integrity assessments on pipeline segments that pass through densely populated areas or near specifically designated high-consequence areas. In January 2012, The Pipeline Safety, Regulatory Certainty and Job Creation Act of 2011 was signed into law. The law increased maximum penalties for violating federal pipeline safety regulations and directs the DOT and Secretary of Transportation to conduct further review or studies on issues that may or may not be material to ONEOK Partners. These issues include, but are not limited to, the following:

In October 2015, PHMSA issued a notice of proposed rule-making to its hazardous liquid pipeline safety regulations. Among other things, the proposed regulations would expand the current leak-detection requirements, apply new, more conservative repair criteria and establish timelines for inspecting pipeline facilities potentially affected by an extreme weather event or natural disaster. The proposal would also increase the stringency of integrity management program requirements and set deadlines for the use of internal inspection tools on certain systems. Comments on the proposed rule-making were due by January 2016. The potential capital and operating expenditures related to the referenced legislation and regulations are unknown, but we do not anticipate a material impact to ONEOK Partners’ planned capital, operations and maintenance costs resulting from compliance with the current or pending regulations.

Air and Water Emissions - The Clean Air Act, the Clean Water Act, analogous state laws and/or regulations promulgated thereunder impose restrictions and controls regarding the discharge of pollutants into the air and water in the United States. Under the Clean Air Act, a federally enforceable operating permit is required for sources of significant air emissions. ONEOK Partners may be required to incur certain capital expenditures for air pollution-control equipment in connection with obtaining or maintaining permits and approvals for sources of air emissions. The Clean Water Act imposes substantial potential liability for the removal of pollutants discharged to waters of the United States and remediation of waters affected by such discharge.

Federal, state and regional initiatives to measure and regulate GHG emissions are underway. ONEOK Partners monitors all relevant federal and state legislation to assess the potential impact on its operations. The EPA’s Mandatory Greenhouse Gas Reporting Rule requires annual GHG emissions reporting from affected facilities and the carbon dioxide emission equivalents for the natural gas delivered by ONEOK Partners and the emission equivalents for all NGLs produced by ONEOK Partners as if all of these products were combusted, even if they are used otherwise.

ONEOK Partners’ 2014 total reported emissions were approximately 45.7 million metric tons of carbon dioxide equivalents. This total includes direct emissions from the combustion of fuel in ONEOK Partners’ equipment, such as compressor engines and heaters, as well as carbon dioxide equivalents from natural gas and NGL products delivered to customers and produced as if all such fuel and NGL products were combusted. The additional cost to gather and report this emission data did not have, and we do not expect it to have, a material impact on our results of operations, financial position or cash flows. In addition, Congress has considered, and may consider in the future, legislation to reduce GHG emissions, including carbon dioxide and methane. Likewise, the EPA may institute additional regulatory rule-making associated with GHG emissions from the oil and natural gas industry. At this time, no rule or legislation has been enacted that assesses any costs, fees or expenses on any of these emissions.

In April 2014, the EPA and the United States Army Corps of Engineers proposed a joint rule-making to redefine the definition of “Waters of the United States” under the Clean Water Act. The final rule was published in June 2015 and became effective on August 28, 2015. Multiple legal actions on the final rule were filed. In October 2015, the Unites States Court of Appeals for the Sixth Circuit entered an order of stay, which is still in effect, and postponed the effect of the final rule nationwide until it decided further proceedings in the case. The final rule is not expected to result in material impacts on ONEOK Partners’ projects, facilities and operations.

The EPA’s “Triggering and Tailoring Rules” regulate GHG emissions at new or modified facilities that meet certain criteria. Affected facilities are required to review best available control technology (BACT) and conduct air-quality analysis, impact analysis and public reviews with respect to such emissions. At current emission threshold levels, this rule has had a minimal impact on ONEOK Partners’ existing facilities. In addition, in June 2014, the Supreme Court of the United States (Supreme Court), in a case styled , Utility Air Regulatory Group v. EPA , 530 U.S. (2014), held that an industrial facility’s potential to emit GHG emissions alone cannot subject a facility to the permitting requirements for major stationary source provisions of the Clean Air Act. The decision invalidated the EPA’s current Triggering and Tailoring Rule for GHG Prevention of Significant Deterioration (PSD) and Title V requirements as applied to facilities considered major sources only for GHGs (referred to as Step 2 sources). However, the Supreme Court also ruled that to the extent a source pursues a capital project (new construction or expansion of existing facility), which otherwise subjects the source to major source PSD permitting for conventional criteria pollutants, the permitting authorities may impose BACT analysis and emission limits for GHGs from those sources.

In April 2015, the United States Court of Appeals for the District of Columbia Circuit (D.C. Circuit), on remand from the Supreme Court, issued its order following the Supreme Court’s decision in Utility Air Regulatory Group v. EPA. The D.C. Circuit’s order: (1) formally vacated EPA regulations implementing the Tailoring Rule to the extent that they require a stationary source to obtain a PSD or Title V permit based solely on the source’s GHG emissions; and (2) ordered the EPA to consider whether any further revisions to its regulations are appropriate in light of the Supreme Court’s decision. In April

2015, the EPA issued a direct final rule to allow for the rescission of Clean Air Act PSD permits issued by the EPA or delegated state and local permitting authorities under Step 2 of the GHG Tailoring Rule. The direct final rule was to become effective unless adverse comments were received by the EPA. In August 2015, the EPA published the direct final rule to confirm that no adverse comments were received and that the rule was now in effect. We do not expect the direct final rule to have a material impact on ONEOK Partners’ existing operations or design decisions for new project applications.

In July 2011, the EPA issued a proposed rule that would change the air emissions New Source Performance Standards, also known as NSPS, and Maximum Achievable Control Technology requirements applicable to the oil and natural gas industry, including natural gas production, processing, transmission and underground storage sectors. In April 2012, the EPA released the final rule, which includes new NSPS and air toxic standards for a variety of sources within natural gas processing plants, oil and natural gas production facilities and natural gas transmission stations. The rule also regulates emissions from the hydraulic fracturing of wells for the first time. The NSPS final rule became effective in October 2012, but the dates for compliance vary and depend in part upon the type of affected facility and the date of construction, reconstruction or modification.

In September 2015, the EPA published several proposed rule-makings that affect the oil and gas industry. The rule-makings included, but were not limited to, proposed amendments to the NSPS rule. The proposed amendments to the NSPS rule included, in part, the proposed direct regulation of methane emissions for the first time as an individual air pollutant from oil and gas sources, as part of the President’s Methane Strategy. The public comments period on the proposed rule-makings ended on December 4, 2015.

In October 2015, the EPA issued a final rule-making to amend downward the National Ambient Air Quality Standards (NAAQS) for ground level ozone. The final rule requires revised designations of the areas in the various states for classification as in attainment or nonattainment for the new ozone NAAQS. Any areas determined to not attain the ozone NAAQS will implicate more strict air permitting requirements for new or modified sources that emit pollutants that contribute to ground level ozone.

At this time we do not anticipate a material impact to our planned capital, operations and maintenance costs resulting from compliance with the current or pending regulations outlined above. However, the EPA may issue additional responses, amendments and/or policy guidance on the final rules, which could alter our present expectations. Generally, the EPA rule-makings will require expenditures for updated emissions controls, monitoring and record-keeping requirements at affected facilities. We do not expect these expenditures will have a material impact on our results of operations, financial position or cash flows.

CERCLA - The federal Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), also commonly known as Superfund, imposes strict, joint and several liability, without regard to fault or the legality of the original act, on certain classes of “persons” (defined under CERCLA) who caused and/or contributed to the release of a hazardous substance into the environment. These persons include, but are not limited to, the owner or operator of a facility where the release occurred and/or companies that disposed or arranged for the disposal of the hazardous substances found at the facility. Under CERCLA, these persons may be liable for the costs of cleaning up the hazardous substances released into the environment, damages to natural resources and the costs of certain health studies. We do not expect ONEOK Partners’ responsibilities under CERCLA will have a material impact on our results of operations, financial position or cash flows.

Chemical Site Security - The United States Department of Homeland Security (Homeland Security) released the Chemical Facility Anti-Terrorism Standards in 2007, and the new final rule associated with these regulations was issued in December 2014. ONEOK Partners provided information regarding its chemicals via Top-Screens submitted to Homeland Security, and its facilities subsequently were assigned one of four risk-based tiers ranging from high (Tier 1) to low (Tier 4) risk, or not tiered at all due to low risk. To date, four of its facilities have been given a Tier 4 rating. Facilities receiving a Tier 4 rating are required to complete Site Security Plans and possible physical security enhancements. We do not expect the Site Security Plans and possible security enhancement costs to have a material impact on our results of operations, financial position or cash flows.

Pipeline Security - The United States Department of Homeland Security’s Transportation Security Administration and the DOT have completed a review and inspection of ONEOK Partners’ “critical facilities” and identified no material security issues. Also, the Transportation Security Administration has released new pipeline security guidelines that include broader definitions for the determination of pipeline “critical facilities.” ONEOK Partners has reviewed its pipeline facilities according to the new guideline requirements, and there have been no material changes required to date.

Environmental Footprint - ONEOK Partners’ environmental and climate change strategy focuses on minimizing the impact of its operations on the environment. These strategies include: (i) developing and maintaining an accurate GHG emissions inventory according to current rules issued by the EPA; (ii) improving the efficiency of its various pipelines, natural gas

processing facilities and natural gas liquids fractionation facilities; (iii) following developing technologies for emissions control and the capture of carbon dioxide to keep it from reaching the atmosphere; and (iv) utilizing practices to reduce the loss of methane from its facilities.

ONEOK Partners participates in the EPA’s Natural Gas STAR Program to reduce voluntarily methane emissions. ONEOK Partners continues to focus on maintaining low rates of lost-and-unaccounted-for methane gas through expanded implementation of best practices to limit the release of natural gas during pipeline and facility maintenance and operations.

No family relationships exist between any of the executive officers, nor is there any arrangement or understanding between any executive officer and any other person pursuant to which the officer was selected.

INFORMATION AVAILABLE ON OUR WEBSITE

We make available, free of charge, on our website (www.oneok.com) copies of our Annual Reports, Quarterly Reports, Current Reports on Form 8-K, amendments to those reports filed or furnished to the SEC pursuant to Section 13(a) or 15(d) of the Exchange Act and reports of holdings of our securities filed by our officers and directors under Section 16 of the Exchange Act as soon as reasonably practicable after filing such material electronically or otherwise furnishing it to the SEC. Copies of our Code of Business Conduct and Ethics, Governance Guidelines, Bylaws and the written charter of our Audit Committee also are available on our website, and we will provide copies of these documents upon request. Our website and any contents thereof are not incorporated by reference into this report.

We also make available on our website the Interactive Data Files required to be submitted and posted pursuant to Rule 405 of Regulation S-T.