Basis of presentation. Access Midstream Partners, L.P., (the “Partnership”) a Delaware limited partnership formed in January 2010, is principally focused on natural gas gathering, the first segment of midstream energy infrastructure that connects natural gas produced at the wellhead to third-party takeaway pipelines. The Partnership is the industry’s largest gathering and processing master limited partnership as measured by throughput volume. The Partnership’s assets are located in Arkansas, Kansas, Louisiana, Maryland, New York, Ohio, Oklahoma, Pennsylvania, Texas, Virginia, West Virginia and Wyoming. The Partnership provides gathering, treating and compression services to Chesapeake Energy Corporation, Total Gas and Power North America, Inc., Statoil ASA, Anadarko Petroleum Corporation, Mitsui & Co., Ltd. and other producers under long-term, fixed-fee contracts.

For purposes of these financial statements, the “Partnership,” when used in a historical context, refers to the financial results of Chesapeake Midstream Partners, L.L.C. through the closing date of our initial public offering (“IPO”) on August 3, 2010 and to Access Midstream Partners, L.P. (NYSE: ACMP) and its subsidiaries thereafter. The “GIP I Entities” refers to, collectively, GIP-A Holding (CHK), L.P., GIP-B Holding (CHK), L.P. and GIP-C Holding (CHK), L.P., the “GIP II Entities” refers to certain entities affiliated with Global Infrastructure Investors II, LLC, and “GIP” refers to the GIP I Entities and their affiliates and the GIP II Entities, collectively. “Williams” refers to The Williams Companies, Inc. (NYSE: WMB). “Chesapeake” refers to Chesapeake Energy Corporation (NYSE: CHK). “Total”, when discussing the upstream joint venture with Chesapeake, refers to Total E&P USA, Inc., a wholly owned subsidiary of Total S.A. (NYSE: TOT, FP: FP), and when discussing our gas gathering agreement and related matters, refers to Total E&P USA, Inc. and Total Gas & Power North America, Inc., a wholly owned subsidiary of Total S.A.

The accompanying consolidated financial statements of the Partnership have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”). To conform to these accounting principles, management makes estimates and assumptions that affect the amounts reported in the consolidated financial statements and the notes thereto. These estimates are evaluated on an ongoing basis, utilizing historical experience and other methods considered reasonable under the particular circumstances. Although these estimates are based on management’s best available knowledge at the time, changes in facts and circumstances or discovery of new facts or circumstances may result in revised estimates and actual results may differ from these estimates. Effects on the Partnership’s business, financial position and results of operations resulting from revisions to estimates are recognized when the facts that give rise to the revision become known.

Offerings and acquisitions.

IPO. On August 3, 2010, the Partnership completed its initial public offering (“IPO”) of 24,437,500 common units (including 3,187,500 common units issued pursuant to the exercise of the underwriters’ over-allotment option on August 3, 2010) at a price of $21.00 per unit. The Partnership’s common units are listed on the New York Stock Exchange (the “NYSE”) under the symbol “ACMP”.

The Partnership received gross offering proceeds in the IPO of approximately $513.2 million less approximately $38.6 million for underwriting discounts and commissions, structuring fees and offering expenses. Pursuant to the terms of the contribution agreement, the Partnership distributed the approximate $62.4 million of net proceeds from the exercise of the over-allotment option to the GIP I Entities on August 3, 2010. Upon completion of the IPO, Chesapeake and the GIP I Entities conveyed to the Partnership a 100 percent membership interest in Chesapeake MLP Operating, L.L.C., which owned all of its assets since September 2009.

During the second quarter of 2012, the GIP II Entities acquired Chesapeake’s 50 percent interest in the Partnership’s general partner and all of the common units and subordinated units in the Partnership that were previously held by Chesapeake. The remaining 50 percent interest in the Partnership’s general partner continued to be owned by the GIP I Entities.

Haynesville Springridge acquisition. On December 21, 2010, the Partnership acquired the Springridge gathering system and related facilities from CMD for $500.0 million. The acquisition was financed with a draw on the Partnership’s revolving credit facility of approximately $234.0 million plus approximately $266.0 million of cash on hand. The Springridge gathering system is primarily located in Caddo and De Soto Parishes, Louisiana. In connection with the acquisition, the Partnership entered into a 10-year, 100 percent fixed-fee gas gathering agreement with Chesapeake which includes a significant acreage dedication, annual fee redetermination and a minimum volume commitment. These assets are referred to collectively as the “Springridge assets” and the acquisition is referred to as the “Springridge acquisition.”

Marcellus acquisition. On December 29, 2011, the Partnership acquired from CMD, all of the issued and outstanding common units of Appalachia Midstream Services, L.L.C. (“Appalachia Midstream”) for total consideration of $879.3 million, consisting of 9,791,605 common units and $600.0 million in cash that was financed with a draw on the Partnership’s revolving credit facility. Through the acquisition of Appalachia Midstream, the Partnership operates 100 percent of and owns an approximate average 47 percent interest in 10 gas gathering systems that consist of approximately 549 miles of gas gathering pipeline in the Marcellus Shale. The remaining 53 percent interest in these assets is owned primarily by Statoil ASA (“Statoil”), Anadarko Petroleum Corporation (“Anadarko”), Epsilon Energy Ltd. (“Epsilon”), Mitsui & Co., Ltd. (“Mitsui”). Appalachia Midstream operates the assets under 15-year fixed fee gathering agreements. The gathering agreements include significant acreage dedications and cost of service mechanisms. EBITDA exceeded the $100 million target in 2012 and no additional revenue related to the commitment was recognized. The target for 2013 represents the minimum amount of EBITDA we will recognize with the potential that throughput for these systems will generate EBITDA in excess of the guaranteed amounts.

CMO acquisition. On December 20, 2012, we acquired from Chesapeake Midstream Development, L.P. (“CMD”), a wholly owned subsidiary of Chesapeake, and certain of CMD’s affiliates, 100 percent of the issued and outstanding equity interests in Chesapeake Midstream Operating, L.L.C. (“CMO”) for total consideration of $2.16 billion (the “CMO Acquisition”). As a result of the CMO Acquisition, the Partnership now owns certain midstream assets in the Eagle Ford, Utica and Niobrara regions. The CMO Acquisition also extended our assets and operations in the Haynesville, Marcellus and Mid-Continent regions. The acquired assets included, in the aggregate, approximately 1,675 miles of pipeline and 4.3 million (gross) dedicated acres as of the date of the acquisition. We also assumed various gas gathering and processing agreements associated with the assets that have terms ranging from 10 to 20 years and that, in certain cases, include cost of service or fee redetermination mechanisms.

Equity Issuance. On December 18, 2012, we completed an equity offering of 18.4 million common units (such amount includes 2.4 million common units issued pursuant to the exercise of the underwriters’ over-allotment option) representing limited partner interest in the Partnership, at a price of $32.15 per common unit.

We received gross offering proceeds (net of underwriting discounts, commissions and offering expenses) from the equity offering of approximately $569.3 million, including the exercise of the option to purchase additional units. We used the net proceeds to pay a portion of the purchase price for the CMO Acquisition.

Subscription Agreement. On December 20, 2012, we sold 5.9 million Class B units to each of the GIP II Entities and Williams and 5.6 million Class C units to each of the GIP II Entities and Williams, in each case pursuant to the subscription agreement. We received aggregate proceeds of approximately $712.1 million in exchange for the sale of Class B units and Class C units, inclusive of the capital contribution made by our general partner to maintain its 2.0 percent interest in the Partnership following the issuance of common, Class B and Class C units.

The results of operations presented and discussed in this annual report include results of operations from CMO for the twelve-day period from closing of the CMO Acquisition on December 20, 2012 through December 31, 2012.

Williams acquisition. Concurrently with the CMO Acquisition, the GIP I Entities sold to Williams 34,538,061 of our subordinated units and 50% of the outstanding equity interests in Access Midstream Ventures, L.L.C., the sole member of our general partner (“Access Midstream Ventures”), for cash consideration of approximately $1.8 billion (the “Williams Acquisition”). The Partnership did not receive any cash proceeds from the Williams Acquisition. As a result of the closing of the Williams Acquisition, the GIP II Entities and Williams together own and control our general partner and the GIP I Entities no longer have any ownership interest in us or our general partner.

Limited partner and general partner units. The following table summarizes common, subordinated, Class B, Class C and general partner units issued during the years ended December 31, 2012, 2011 and 2010:

Holdings of partnership equity. At December 31, 2012, the GIP II Entities held 1,933,244 notional general partner units representing a 1.0 percent general partner interest in the Partnership, 50 percent of the Partnership’s incentive distribution rights, 33,704,666 common units, 34,538,061 subordinated units, 5,929,025 Class B units and 5,599,634 Class C units. The GIP II Entities’ ownership represents an aggregate 41.3 percent limited partner interest in the Partnership. Williams held 1,933,244 notional general partner units representing a 1.0 percent general partner interest in the Partnership, 50.0 percent of the Partnership’s incentive distribution rights, 34,538,061 subordinated units, 5,929,025 Class B units and 5,599,634 Class C units. Williams ownership represents an aggregate 23.8 percent limited partner interest in the Partnership. The public held 63,619,787 common units, representing a 32.9 percent limited partner interest in the Partnership.

Use of estimates. The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts and disclosure of contingencies. Significant estimates include: (1) estimated useful lives of assets, which impacts depreciation and amortization; (2) accruals related to revenues, expenses and capital costs; (3) liability and contingency accruals; and (4) cost allocations as described in Note 5. Although management believes these estimates are reasonable, actual results could differ from the Partnership’s estimates.

Cash and cash equivalents. For purposes of the consolidated financial statements, investments in all highly liquid instruments with original maturities of three months or less at date of purchase are considered to be cash equivalents. The Partnership had approximately $65.0 million and $22.0 thousand of cash and cash equivalents as of December 31, 2012 and 2011, respectively. Book overdrafts are checks that have been issued before the end of the period, but not presented to the bank for payment before the end of the period. At December 31, 2012 and 2011, book overdrafts of $30.0 million and $8.5 million, respectively, were included in accounts payable.

Accounts receivable. The majority of accounts receivable relate to gathering and treating activities. Accounts receivable included in the balance sheets are reflected net of an allowance for doubtful accounts, if warranted. At December 31, 2012, the Partnership had no allowance for doubtful accounts. At December 31, 2011, the Partnership had an allowance for doubtful accounts of $0.4 million.

Property, plant and equipment. Property, plant and equipment are recorded at cost. Expenditures for maintenance and repairs that do not add capacity or extend the useful life of an asset are expensed as incurred. The carrying value of the assets is based on estimates, assumptions and judgments relative to useful lives and salvage values. As assets are disposed of, the cost and related accumulated depreciation are removed from the accounts, and any resulting gain or loss is included in operating expenses in the statements of operations.

Certain of the gathering systems of the Partnership are subject to an agreement with a subsidiary of Chesapeake that provides the Partnership rights and obligations equivalent to a capital lease. Under the terms of the agreement, the Partnership has rights to the associated capital assets for as long as the assets are in operation. Specifically, the Partnership will pay all costs associated with the related gathering systems, including all capital costs, operating costs and direct and indirect overhead costs. In exchange for paying such costs and for the services it provides pursuant to the agreement, the Partnership receives revenues derived from operation of the gathering systems. At December 31, 2012 and 2011, approximately $125.6 million and $124.5 million ($99.8 million and $105.0 million net of accumulated depreciation), respectively, of the Partnership’s gathering system assets were held under such agreement. Payments for capital costs under the agreement are made as the associated capital assets are constructed and, accordingly, as of December 31, 2012, the Partnership had no capital lease obligation liability associated with the assets held under the agreement.

Depreciation is calculated using the straight-line method, based on the assets’ estimated useful lives. These estimates are based on various factors including age (in the case of acquired assets), manufacturing specifications, technological advances and historical data concerning useful lives of similar assets.

Impairment of long-lived assets. Long-lived assets with recorded values that are not expected to be recovered through future cash flows are written down to estimated fair value. Assets are tested for impairment when events or circumstances indicate that the carrying value may not be recoverable. The carrying value of a long-lived asset is not recoverable if it exceeds the sum of the undiscounted cash flows expected to result from the use and eventual disposition of the asset. If the carrying value exceeds the sum of the undiscounted cash flows, an impairment loss equal to the amount that the carrying value exceeds the fair value of the asset is recognized. Fair value is determined using an income approach whereby the expected future cash flows are discounted using a rate management believes a market participant would assume is reflective of the risks associated with achieving the underlying cash flows.

Equity Method Investments. The equity method of accounting is used to account for the Partnership’s interest in Utica East Ohio Midstream LLC and Ranch Westex JV, LLC, which the Partnership acquired as part of the CMO Acquisition. The equity method is also used to account for the Partnership’s various ownership interests in 10 gas gathering systems in the Marcellus Shale. See Note 1 – Description of Business and Basis of Presentation for more information on the acquisitions.

Asset retirement obligations. Management recognizes a liability based on the estimated costs of retiring tangible long-lived assets. The liability is recognized at the Partnership’s fair value measured using expected discounted future cash outflows of the asset retirement obligation when the obligation originates, which generally is when an asset is acquired or constructed. The carrying amount of the associated asset is increased commensurate with the liability recognized. Accretion expense is recognized over time as the discounted liability is accreted to the Partnership’s expected settlement value. Subsequent to the initial recognition, the liability is adjusted for any changes in the expected value of the retirement obligation (with a corresponding adjustment to property, plant and equipment) and for accretion of the liability due to the passage of time, until the obligation is settled. If the fair value of the estimated asset retirement obligation changes, an adjustment is recorded for both the asset retirement obligation and the associated asset carrying amount. Revisions in estimated asset retirement obligations may result from changes in estimated inflation rates, discount rates, retirement costs and the estimated timing of settling asset retirement obligations.

Fair value. The fair-value-measurement standard defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The standard characterizes inputs used in determining fair value according to a hierarchy that prioritizes those inputs based upon the degree to which they are observable. The three levels of the fair value hierarchy are as follows:

Level 1—inputs represent quoted prices in active markets for identical assets or liabilities.

Level 2—inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly (for example, quoted market prices for similar assets or liabilities in active markets or quoted market prices for identical assets or liabilities in markets not considered to be active, inputs other than quoted prices that are observable for the asset or liability, or market-corroborated inputs).

Level 3—inputs that are not observable from objective sources, such as management’s internally developed assumptions used in pricing an asset or liability (for example, an estimate of future cash flows used in management’s internally developed present value of future cash flows model that underlies the fair value measurement).

Nonfinancial assets and liabilities initially measured at fair value include third-party business combinations, impaired long-lived assets (asset groups), and initial recognition of asset retirement obligations.

The fair value of debt is the estimated amount the Partnership would have to pay to repurchase its debt, including any premium or discount attributable to the difference between the stated interest rate and market rate of interest at the balance sheet date. Fair values are based on quoted market prices or average valuations of similar debt instruments at the balance sheet date for those debt instruments for which quoted market prices are not available. See Note 11—Debt and Interest Expense for disclosures regarding the fair value of debt.

The carrying amount of cash and cash equivalents, accounts receivable and accounts payable reported on the balance sheet approximates fair value.

Segments. The Partnership’s operations are organized into a single business segment, the assets of which consist of natural gas gathering systems, treating facilities, processing facilities, pipelines and related plant and equipment.

Revenue Recognition. In 2012, the Partnership derived the majority of its revenues through gas gathering agreements with Chesapeake and Total. Pursuant to their respective applicable gas gathering agreements, Chesapeake and Total have agreed to minimum volume commitments covering production in the Barnett Shale region for each year through December 31, 2018 and for the six month period ending June 30, 2019, and, solely with respect to Chesapeake, in the Haynesville Shale region for each year through December 31, 2013 and December 31, 2017 for the Springridge and Mansfield systems, respectively. In the event either Chesapeake or Total does not meet its minimum volume commitment to the Partnership in the Barnett Shale region or Chesapeake does not meet its minimum volume commitment to the Partnership in the Haynesville Shale region, for any annual period (or six month period with respect to the six months ending June 30, 2019 in the Barnett Shale region) during the minimum volume commitment period, Chesapeake and Total will be obligated to pay a fee equal to the applicable fee for each Mcf by which the applicable party’s minimum volume commitment for such year (or six month period with respect to the six months ending June 30, 2019) exceeds the actual volumes gathered from such party’s production. The revenue associated with such shortfall fees is recognized in the fourth quarter of each year.

Revenues consist of fees recognized for the gathering, treating, compression and processing of natural gas. Revenues are recognized when the service is performed and is based upon non-regulated rates and the related gathering, treating, compression and processing volumes.

Deferred Loan Costs. External costs incurred in connection with closing the revolving bank credit facilities are capitalized as deferred loan costs and amortized over the life of the related agreement. Amortization is included in interest expense in the statement of operations.

Environmental Expenditures. Liabilities for loss contingencies, including environmental remediation costs, arising from claims, assessments, litigation, fines, and penalties and other sources are charged to expense when it is probable that a liability has been incurred and the amount of the assessment and/or remediation can be reasonably estimated. There are no liabilities reflected in the accompanying financial statements at December 31, 2012 and 2011.

Equity Based Compensation. Through December 31, 2012, certain employees of Chesapeake were seconded to the Partnership and provided operating, routine maintenance and other services with respect to the business under the direction, supervision and control of the Partnership’s general partner. A number of these employees received equity-based compensation through Chesapeake’s stock-based compensation programs, which consist of restricted stock issued to employees.

The fair value of the awards issued was determined based on the fair market value of the shares on the date of grant. However, the Partnership’s expense was allocated based on the lesser of the value at grant date or vest date. This value is amortized over the vesting period, which is generally four or five years from the date of grant. To the extent compensation cost relates to employee activities directly involved in gathering or treating operations, such amounts were charged to the Partnership and its predecessor and were reflected as operating expenses. Included in operating expenses is stock-based compensation of $9.0 million, $3.8 million and $2.1 million for the Partnership during the years ended December 31, 2012, 2011 and 2010, respectively. To the extent compensation cost relates to employees indirectly involved in gathering or treating operations, such amounts are charged to the Partnership and its predecessor through an overhead allocation and are reflected as general and administrative expenses.

The Access Midstream Long-Term Incentive Plan (“LTIP”) provides for an aggregate of 3,500,000 common units to be awarded to employees, directors and consultants of the Partnership’s general partner and its affiliates through various award types, including unit awards, restricted units, phantom units, unit options, unit appreciation rights and other unit-based awards. The LTIP has been designed to promote the interests of the Partnership and its unitholders by strengthening its ability to attract, retain and motivate qualified individuals to serve as employees, directors and consultants. As of December 31, 2012, there was $11.5 million of unrecognized compensation expense attributable to the LTIP, of which $10.7 million is expected to be recognized over a weighted average period of four years.

The following table summarizes LTIP award activity for the year ended December 31, 2012:

Intangible Assets. Intangible assets are generally amortized on a straight-line basis over their estimated useful lives, unless the assets economic benefits are consumed on an other than straight-line basis. The estimated useful life is the period over which the assets are expected to contribute directly or indirectly to the Partnership’s future cash flows. The estimated useful life of the customer relationship acquired with the Springridge gathering system and Appalachia Midstream is 15 years and 20 years for the CMO Acquisition. Amortization expense was $11.3 million and $11.3 million for the years ended December 31, 2012 and 2011, respectively, for the Partnership. No amortization expense was recognized for the year ended December 31, 2010.

The Partnership assesses long-lived assets, including property, plant and equipment and intangible assets, for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is assessed by comparing the carrying amount of an asset to undiscounted future net cash flows expected to be generated by the asset. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amounts exceed the fair value of the assets.

Business Combinations. The Partnership makes various assumptions in developing models for determining the fair values of assets and liabilities associated with business acquisitions. These fair value models, developed with the assistance of outside consultants, apply discounted cash flow approaches to expected future operating results, considering expected growth rates, development opportunities, and future pricing assumptions to arrive at an economic value for the business acquired. The Partnership then determines the fair value of the tangible assets based on estimates of replacement costs less obsolescence. Identifiable intangible assets acquired consist primarily of customer contracts, customer relationships, trade names, and licenses and permits. The Partnership values customer relationships using a discounted cash flow model.

Income taxes. As a master limited partnership, the Partnership is a pass-through entity and also not subject to federal income taxes and most state income taxes with the exception of Texas Franchise Tax. For federal and state income tax purposes, all income, expenses, gains, losses and tax credits generate flow through to the owners, and accordingly, do not result in a provision for income taxes.

Variable Interest Entities (VIEs). An entity is referred to as a VIE pursuant to accounting guidance for consolidation if it possesses one of the following criteria: (i) it is thinly capitalized, (ii) the residual equity holders do not control the entity, (iii) the equity holders are shielded from the economic losses, (iv) the equity holders do not participate fully in the entity’s residual economics, or (v) the entity was established with non-substantive voting interests. We consolidate a VIE when we have both the power to direct the activities that most significantly impact the activities of the VIE and the right to receive benefits or the obligation to absorb losses of the entity that could be potentially significant to the VIE. We continually monitor both consolidated and unconsolidated VIEs to determine if any events have occurred that could cause the primary beneficiary to change.