Note 1 – Nature of Operations and Basis of Presentation

Nature of Operations.  Southwest Gas Corporation and its subsidiaries (the “Company”) consist of two segments: natural gas operations (“Southwest” or the “natural gas operations” segment) and construction services. Southwest is engaged in the business of purchasing, distributing, and transporting natural gas for customers in portions of Arizona, Nevada, and California. Public utility rates, practices, facilities, and service territories of Southwest are subject to regulatory oversight. The timing and amount of rate relief can materially impact results of operations. Natural gas purchases and the timing of related recoveries can materially impact liquidity. Results for the natural gas operations segment are higher during winter periods due to the seasonality incorporated in its regulatory rate structures. Centuri Construction Group, Inc. (“Centuri” or the “construction services” segment), a 96.6% owned subsidiary, is a full-service underground piping contractor that primarily provides utility companies with trenching and installation, replacement, and maintenance services for energy distribution systems, and industrial construction solutions. Centuri operations are generally conducted under the business names of NPL Construction Co. (“NPL”), NPL Canada Ltd. (“NPL Canada”, formerly Link-Line Contractors Ltd.), W.S. Nicholls Construction, Inc. and related companies (“W.S. Nicholls”), and Brigadier Pipelines Inc. (“Brigadier”). In May 2016, Centuri completed the acquisition of two privately held, affiliated construction businesses by means of asset purchase: Enterprise Trenchless Technologies, Inc. and ETTI Holdings (collectively, “ETTI”). See Acquisition of Construction Services Businesses below for more information. Typically, Centuri revenues are lowest during the first quarter of the year due to unfavorable winter weather conditions. Operating revenues typically improve as more favorable weather conditions occur during the summer and fall months.

Basis of Presentation.  The condensed consolidated financial statements included herein have been prepared by the Company, without audit, pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). Certain information and footnote disclosures normally included in financial statements prepared in accordance with United States generally accepted accounting principles (“U.S. GAAP”) have been condensed or omitted pursuant to such rules and regulations. The preparation of the condensed consolidated financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. In the opinion of management, all adjustments, consisting of normal recurring items and estimates necessary for a fair presentation of results for the interim periods, have been made. It is suggested that these condensed consolidated financial statements be read in conjunction with the consolidated financial statements and the notes thereto included in the 2015 Annual Report to Shareholders, which is incorporated by reference into the 2015 Form 10-K.

During the third quarter of 2016, Centuri evaluated the estimated useful lives of its depreciable assets, and in so doing determined that certain equipment lives should be extended. This change in estimate reduced current-quarter depreciation by approximately $2 million.

Prepaids and other current assets.  Prepaids and other current assets includes gas pipe materials and operating supplies of $30 million at September 30, 2016 and $24 million at December 31, 2015 (carried at weighted average cost), and also includes natural gas stored underground and liquefied natural gas, in addition to prepaid assets.

Cash and Cash Equivalents.  For purposes of reporting consolidated cash flows, cash and cash equivalents include cash on hand and financial instruments with a purchase-date maturity of three months or less. In general, cash and cash equivalents fall within Level 1 (quoted prices for identical financial instruments) of the three-level fair value hierarchy that ranks the inputs, used to measure fair value, by their reliability. However, cash and cash equivalents at September 30, 2016 and December 31, 2015 also include money market fund investments totaling approximately $68.3 million and $250,000, respectively, which fall within Level 2 (significant other observable inputs) of the fair value hierarchy, due to the asset valuation methods used by money market funds.

Significant non-cash investing and financing activities for the natural gas operations segment included the following: Upon contract expiration, customer advances of approximately $3.6 million and $2.8 million, during the first nine months of 2016 and 2015, respectively, were applied as contributions toward utility construction activity and represent non-cash investing activity.

6

Goodwill. Goodwill is assessed as of October each year for impairment, or otherwise, if circumstances indicate impairment to the carrying value of goodwill may have occurred. No such circumstances indicating impairment were deemed to have occurred in the first nine months of 2016. The business acquisition of ETTI was deemed an asset purchase for tax purposes. As a result, approximately $11 million in goodwill associated with ETTI is expected to be tax deductible.

Acquisition of Construction Services Businesses.   In May 2016, Centuri completed the acquisition of ETTI, which is based in Lisbon Falls, Maine, and has a primary focus on underground utility installation using horizontal directional drilling technology. The acquisition of ETTI will provide complementary operational support to Brigadier and expand operations into Maine. Neither the acquisition itself nor the impacts to assets and operations are material to the construction services segment or the Company.

Assets acquired in the transaction were recorded at their acquisition date fair values. The final purchase accounting has not yet been completed. Further refinement could occur; however, no material changes are expected. The preliminary estimated fair values of assets acquired as of May 6, 2016, the acquisition date, are as follows (in millions of dollars):

The purchase price consisted of $17 million in cash on the acquisition date with the remaining amount being deferred over four years.

Intercompany Transactions . Centuri recognizes revenues generated from contracts with Southwest (see Note 3 - Segment Information below). Centuri’s accounts receivable for these services are presented in the table below (thousands of dollars):

The accounts receivable balance, revenues, and associated profits are included in the condensed consolidated financial statements of the Company and were not eliminated during consolidation in accordance with accounting treatment for rate-regulated entities.

7

Other Property and Investments.   Other property and investments includes (thousands of dollars):

Other Income (Deductions).   The following table provides the composition of significant items included in Other income (deductions) in the condensed consolidated statements of income (thousands of dollars):

Included in the table above is the change in cash surrender values of company-owned life insurance (“COLI”) policies (including net death benefits recognized). These life insurance policies on members of management and other key employees are used by Southwest to indemnify itself against the loss of talent, expertise, and knowledge, as well as to provide indirect funding for certain nonqualified benefit plans. Current tax regulations provide for tax-free treatment of life insurance (death benefit) proceeds. Therefore, changes in the cash surrender values of COLI policies, as they progress towards the ultimate death benefits, are also recorded without tax consequences.

Income taxes.  The Company claimed a federal income tax credit, which resulted in a recognized benefit of approximately $1.6 million during the third quarter of 2016.

Recently Issued Accounting Standards Updates.  In May 2014, the Financial Accounting Standards Board (“FASB”) issued the update “Revenue from Contracts with Customers (Topic 606).” The update replaces much of the current guidance regarding revenue recognition including most industry-specific guidance. In accordance with the update, an entity will be required to identify the contract with the customer, identify the performance obligations in the contract, determine the transaction price, allocate the transaction price to the performance obligations in the contract, and recognize revenue when (or as) the entity satisfies a performance obligation. In addition to the new revenue recognition requirements, entities will be required to disclose sufficient information to enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. Entities may choose between two retrospective transition methods when applying the update. In July 2015, the FASB approved a one-year deferral of the effective date (annual periods beginning after December 15, 2017) and permitted entities to adopt one year earlier (i.e., the original effective date) if they choose. In March, April, and May of 2016, the FASB issued the updates “Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net)”, “Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing”, and “Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients”. The amendments in the first two updates, respectively, provide guidance when another party, along with the entity, is involved in providing a good or service to a customer, and provide clarification with regard to identifying performance obligations and of the licensing implementation guidance in Topic 606. The third update includes narrow-scope improvements to the guidance on collectability, noncash consideration, and completed contracts at transition. In addition, a practical expedient is provided for contract modifications at transition and an accounting policy election related to the presentation of sales taxes and other similar taxes collected from customers. The combined amendments do not change the core principle of the guidance in Topic 606. The Company plans to adopt all of these updates at the required adoption date, which is for interim and annual reporting periods commencing January 1, 2018. The Company is evaluating what impact these updates might have on its consolidated financial statements and disclosures.

8

In August 2014, the FASB issued the update “Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern,” which requires management to assess a company’s ability to continue as a going concern and to provide related footnote disclosures in certain circumstances. Under the update, disclosures are required when conditions give rise to substantial doubt about a company’s ability to continue as a going concern within one year from the financial statement issuance date. The update is effective for the annual period ending after December 15, 2016, and all annual and interim periods thereafter. This update and changes thereto are not expected to have a material impact on the Company’s disclosures.

In January 2016, the FASB issued the update “Financial Instruments – Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities” in order to improve the recognition and measurement of financial instruments. The update makes targeted improvements to existing U.S. GAAP by: 1) requiring equity investments to be measured at fair value with changes in fair value recognized in net income; 2) requiring the use of the exit price notion when measuring the fair value of financial instruments for disclosure purposes; 3) requiring separate presentation of financial assets and financial liabilities by measurement category and form of financial asset on the balance sheet or the accompanying notes to the financial statements; 4) eliminating the requirement to disclose the method(s) and significant assumptions used to estimate the fair value that is required to be disclosed for financial instruments measured at amortized cost on the balance sheet; and 5) requiring a reporting entity to present separately in other comprehensive income the portion of the total change in the fair value of a liability resulting from a change in instrument-specific credit risk when the organization has elected to measure the liability at fair value in accordance with the fair value option for financial instruments. The update is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. All entities can early adopt the provision to record fair value changes for financial liabilities under the fair value option resulting from instrument-specific credit risk in other comprehensive income. The Company is evaluating what impact, if any, this update might have on its consolidated financial statements and disclosures.

In February 2016, the FASB issued the update “Leases (Topic 842)”. Under the update, lessees will be required to recognize the following for all leases (with the exception of short-term leases) at the commencement date:

Under the new guidance, lessor accounting is largely unchanged. Certain targeted improvements were made to align, where necessary, lessor accounting with the lessee accounting model and Topic 606, Revenue from Contracts with Customers. Though companies have historically been required to make disclosures regarding leases and of contractual obligations, leases (with terms longer than a year) will no longer exist off-balance sheet. Lessees (for capital and operating leases) and lessors (for sales-type, direct financing, and operating leases) must apply a modified retrospective transition approach for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. The modified retrospective approach would not require any transition accounting for leases that expired before the earliest comparative period presented. Lessees and lessors may not apply a full retrospective transition approach. Early application is permitted. The Company currently plans to adopt the update at the required adoption date, which is for interim and annual reporting periods commencing January 1, 2019. The Company is evaluating what impact this update might have on its consolidated financial statements and disclosures.

In March 2016, the FASB issued the update “Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting”. The amendments are intended to improve the accounting for employee share-based payments and affect all organizations that issue share-based payment awards to their employees. The update requires the recording of all of the tax effects related to share-based payments at settlement (or expiration) through the income statement. Currently, tax benefits in excess of compensation cost (“windfalls”) are recorded in equity, and tax deficiencies (“shortfalls”) are recorded in equity to the extent of previous windfalls, and then recorded in the income statement. While the simplification will reduce some of the administrative complexities by eliminating the need to track a “windfall pool,” it will increase the volatility of income tax expense. The update also allows entities to withhold shares for the employee tax burden up to the employees’ maximum individual tax rate in the relevant jurisdiction without resulting in a liability classification of the award (currently such withholding is limited to the employer’s minimum statutory withholding). The update clarifies that all cash payments made to taxing authorities

9

on the employees’ behalf for withheld shares should be presented as financing activities on the statement of cash flows. Also, the update requires all tax-related cash flows resulting from share-based payments be reported as operating activities on the statement of cash flows, a change from the current requirement to present windfall tax benefits as an inflow from financing activities and an outflow from operating activities. The update is effective for fiscal years beginning after December 15, 2016, including interim periods within those fiscal years. Early adoption is permitted. The Company issues share-based payment awards to its employees and is evaluating the impacts this update might have on its consolidated financial statements and disclosures.

In June 2016, the FASB issued the update “Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments”. The update amends guidance on reporting credit losses for financial assets held at amortized cost basis and available for sale debt securities. For assets held at amortized cost basis, the update eliminates the “probable” threshold for initial recognition of credit losses in current U.S. GAAP and, instead, requires an entity to reflect its current estimate of all expected credit losses. The allowance for credit losses is a valuation account that is deducted from the amortized cost basis of the financial asset to present the net amount expected to be collected. For available for sale debt securities, credit losses should be measured in a manner similar to current U.S. GAAP, however the update will require that credit losses be presented as an allowance rather than as a write-down. This update affects entities holding financial assets and net investment in leases that are not accounted for at fair value through net income. The update affects loans, debt securities, trade receivables, net investments in leases, off-balance sheet credit exposures, reinsurance receivables, and any other financial assets not excluded from the scope that have the contractual right to receive cash. The update is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. All entities may adopt the amendments in this update earlier as of fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. The Company is evaluating what impact, if any, this update might have on its consolidated financial statements and disclosures.

In August 2016, the FASB issued the update “Classification of Certain Cash Receipts and Cash Payments”. This update addresses the following eight specific cash flow issues: debt prepayment or debt extinguishment costs; settlement of zero-coupon debt instruments or other debt instruments with coupon interest rates that are insignificant in relation to the effective interest rate of the borrowing; contingent consideration payments made after a business combination; proceeds from the settlement of insurance claims; proceeds from the settlement of corporate-owned life insurance (“COLI”) policies; distributions received from equity method investees; beneficial interests in securitization transactions; and separately identifiable cash flows, including identification of the predominant nature in cases where cash receipts and payments have aspects of more than one class of cash flows. The update is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption is permitted. The Company is evaluating the impacts this update might have on its consolidated cash flow statements and disclosures.

In October 2016, the FASB issued the update “Accounting for Income Taxes: Intra-Entity Asset Transfers of Assets Other than Inventory.” This update eliminates the current U.S. GAAP exception for all intra-entity sales of assets other than inventory. As a result, a reporting entity would recognize the tax expense from the sale of the asset in the seller’s tax jurisdiction when the transfer occurs, even though the pre-tax effects of that transaction are eliminated in consolidation. Any deferred tax asset that arises in the buyer’s jurisdiction would also be recognized at the time of the transfer. The update is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption is permitted; however, the guidance can only be adopted in the first interim period of a fiscal year. The modified retrospective approach will be required for transition to the new guidance, with a cumulative-effect adjustment recorded in retained earnings as of the beginning of the period of adoption. The Company is evaluating the impacts this update might have on its consolidated financial statements.

In October 2016, the FASB issued the update “Consolidation (Topic 810): Interests Held through Related Parties That Are under Common Control.” The amendments affect reporting entities that are required to evaluate whether they should consolidate a variable interest entity in certain situations involving entities under common control. The update is effective for fiscal and interim periods beginning after December 15, 2016. Early adoption is permitted. The Company is evaluating what impacts, if any, this update might have on its consolidated financial statements.

10

Note 2 – Components of Net Periodic Benefit Cost

Southwest has a noncontributory qualified retirement plan with defined benefits covering substantially all employees and a separate unfunded supplemental retirement plan (“SERP”), which is limited to officers. Southwest also provides postretirement benefits other than pensions (“PBOP”) to its qualified retirees for health care, dental, and life insurance.

During the third quarter of 2016, qualifying term-vested participants were offered a lump-sum present value payout of their pensions. The offer was primarily intended to reduce insurance and ongoing maintenance costs associated with qualifying participant balances. About one-half of the approximate 800 participants subject to the offer accepted the offer, resulting in an approximate $30 million payment from pension assets to be made in the fourth quarter of 2016. This lump sum payout will have no impact on net periodic benefit cost or pension funding requirements during 2016.

Net periodic benefit costs included in the table below are components of an overhead loading process associated with the cost of labor. The overhead process ultimately results in allocation of net periodic benefit costs to the same accounts to which productive labor is charged. As a result, net periodic benefit costs become components of various accounts, primarily operations and maintenance expense, net utility plant, and deferred charges and other assets.

11

12

Note 4 – Derivatives and Fair Value Measurements

Derivatives.  In managing its natural gas supply portfolios, Southwest has historically entered into fixed- and variable-price contracts, which qualify as derivatives. Additionally, Southwest utilizes fixed-for-floating swap contracts (“Swaps”) to supplement its fixed-price contracts. The fixed-price contracts, firm commitments to purchase a fixed amount of gas in the future at a fixed price, qualify for the normal purchases and normal sales exception that is allowed for contracts that are probable of delivery in the normal course of business, and are exempt from fair value reporting. The variable-price contracts have no significant market value. The Swaps are recorded at fair value.

The fixed-price contracts and Swaps are utilized by Southwest under its volatility mitigation programs to effectively fix the price on a portion (up to 25% in the Arizona and California jurisdictions) of its natural gas supply portfolios. The maturities of the Swaps highly correlate to forecasted purchases of natural gas, during time frames ranging from October 2016 through March 2018. Under such contracts, Southwest pays the counterparty a fixed rate and receives from the counterparty a floating rate per MMBtu (“dekatherm”) of natural gas. Only the net differential is actually paid or received. The differential is calculated based on the notional amounts under the contracts, which are detailed in the table below (thousands of dekatherms):

Southwest does not utilize derivative financial instruments for speculative purposes, nor does it have trading operations.

The following table sets forth the gains and (losses) recognized on the Company’s Swaps (derivatives) for the three-, nine-, and twelve-month periods ended September 30, 2016 and 2015 and their location in the Condensed Consolidated Statements of Income:

Gains (losses) recognized in income for derivatives not designated as hedging instruments:

(Thousands of dollars)

No gains (losses) were recognized in net income or other comprehensive income during the periods presented for derivatives designated as cash flow hedging instruments. Previously, Southwest entered into two forward-starting interest rate swaps (“FSIRS”), both of which were designated cash flow hedges, to partially hedge the risk of interest rate variability during the period leading up to the planned issuance of debt. The first FSIRS terminated in December 2010, and the second, in March 2012. Losses on both FSIRS are being amortized over ten-year periods from Accumulated other comprehensive income (loss) into interest expense.

13

The following table sets forth, the fair values of the Company’s Swaps and their location in the Condensed Consolidated Balance Sheets (thousands of dollars):

Fair values of derivatives not designated as hedging instruments:

The estimated fair values of the natural gas derivatives were determined using future natural gas index prices (as more fully described below). The Company has master netting arrangements with each counterparty that provide for the net settlement (in the settlement month) of all contracts through a single payment. As applicable, the Company has elected to reflect the net amounts in its balance sheets. The Company had no outstanding collateral associated with the Swaps during any period presented in the above table.

Pursuant to regulatory deferral accounting treatment for rate-regulated entities, Southwest records the unrealized gains and losses in fair value of the Swaps as a regulatory asset and/or liability. When the Swaps mature, Southwest reverses any prior positions held and records the settled position as an increase or decrease of purchased gas under the related purchased gas adjustment (“PGA”) mechanism in determining its deferred PGA balances. Neither changes in fair value, nor settled amounts, of Swaps have a direct effect on earnings or other comprehensive income.

The following table shows the amounts Southwest paid to counterparties for settlements of matured Swaps.

The following table details the regulatory assets/(liabilities) offsetting the derivatives at fair value in the Condensed Consolidated Balance Sheets (thousands of dollars).

14

Fair Value Measurements.  The estimated fair values of Southwest’s Swaps were determined at September 30, 2016 and December 31, 2015 using New York Mercantile Exchange (“NYMEX”) futures settlement prices for delivery of natural gas at Henry Hub adjusted by the price of NYMEX ClearPort basis Swaps, which reflect the difference between the price of natural gas at a given delivery basin and the Henry Hub pricing points. These Level 2 inputs (inputs, other than quoted prices, for similar assets or liabilities) are observable in the marketplace throughout the full term of the Swaps, but have been credit-risk adjusted with no significant impact to the overall fair value measurement.

The following table sets forth, by level within the three-level fair value hierarchy that ranks the inputs used to measure fair value by their reliability, the Company’s financial assets and liabilities that were accounted for at fair value:

Level 2 - Significant other observable inputs