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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-Q

x      QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the quarterly period ended June 30, 2012

OR

o         TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

Commission file number: 1-34722

PAA Natural Gas Storage, L.P.

(Exact name of registrant as specified in its charter)

(713) 646-4100

(Registrant’s telephone number, including area code)

Indicate by check mark whether the registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.  x Yes  o No

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate website, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).  x Yes  o No

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act. (Check one):

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).  o Yes  x No

As of August 2, 2012, there were 59,193,825 common units outstanding.

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PAA NATURAL GAS STORAGE, L.P. AND SUBSIDIARIES

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PART I. FINANCIAL INFORMATION

Item 1. UNAUDITED CONDENSED CONSOLIDATED FINANCIAL STATEMENTS

PAA Natural Gas Storage, L.P. and Subsidiaries

Condensed Consolidated Balance Sheets

(in thousands, except units)

The accompanying notes are an integral part of these unaudited condensed consolidated financial statements.

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PAA Natural Gas Storage, L.P. and Subsidiaries

Condensed Consolidated Statements of Operations

(in thousands, except per unit data)

(1) Excludes Series B subordinated units. See Note 8, “Net Income per Limited Partner Unit.”

The accompanying notes are an integral part of these unaudited condensed consolidated financial statements.

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PAA Natural Gas Storage, L.P. and Subsidiaries

Condensed Consolidated Statements of Comprehensive Income

(in thousands)

PAA Natural Gas Storage, L.P. and Subsidiaries

Condensed Consolidated Statement of Changes in Accumulated Other Comprehensive Income/(Loss)

(in thousands)

The accompanying notes are an integral part of these unaudited condensed consolidated financial statements.

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PAA Natural Gas Storage, L.P. and Subsidiaries

Condensed Consolidated Statements of Cash Flows

(in thousands)

The accompanying notes are an integral part of these unaudited condensed consolidated financial statements.

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PAA Natural Gas Storage, L.P. and Subsidiaries

Condensed Consolidated Statement of Changes in Partners’ Capital

(in thousands)

The accompanying notes are an integral part of these unaudited condensed consolidated financial statements.

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PAA Natural Gas Storage, L.P. and Subsidiaries

Notes to the Condensed Consolidated Financial Statements

(unaudited)

Note 1—Organization and Basis of Presentation

PAA Natural Gas Storage, L.P. (the “Partnership” or “PNG”) is a Delaware limited partnership formed on January 15, 2010 to own the natural gas storage business of Plains All American Pipeline, L.P. (“PAA”). The Partnership is a fee-based, growth-oriented partnership engaged in the ownership, acquisition, development, operation and commercial management of natural gas storage facilities.

We currently own and operate three natural gas storage facilities located in Louisiana, Mississippi and Michigan. Our Pine Prairie and Southern Pines facilities are recently constructed, high-deliverability salt cavern natural gas storage complexes located in Evangeline Parish, Louisiana and Greene County, Mississippi, respectively. Our Bluewater facility is a depleted reservoir natural gas storage complex located approximately 50 miles from Detroit in St. Clair County, Michigan. As of June 30, 2012, through these facilities, PNG had a total of eight operational salt storage caverns and two depleted reservoirs used for natural gas storage, with an aggregate owned working gas storage capacity of approximately 86 billion cubic feet (“Bcf”). We also own PNG Marketing, LLC, a wholly owned commercial optimization company, that captures short-term market opportunities by leasing a portion of our storage capacity and engaging in related commercial marketing activities.

As of June 30, 2012, PAA owned approximately 64% of the equity interests in the Partnership, including our 2.0% general partner interest and limited partner interests consisting of 28,155,526 common units, 11,934,351 Series A subordinated units and 13,500,000 Series B subordinated units.

The accompanying condensed consolidated interim financial statements include the accounts of PNG and its subsidiaries, all of which are wholly owned, and should be read in conjunction with our consolidated financial statements and notes thereto presented in our 2011 Annual Report on Form 10-K. The financial statements have been prepared in accordance with the instructions for interim reporting as prescribed by the SEC. All adjustments (consisting only of normal recurring adjustments) that in the opinion of management were necessary for a fair statement of the results for the interim periods have been reflected. All significant intercompany transactions have been eliminated in consolidation, and certain reclassifications have been made to information from previous years to conform to the current presentation. These reclassifications do not affect net income attributable to the Partnership. The condensed balance sheet data as of December 31, 2011 was derived from audited financial statements, but does not include all disclosures required by U.S. GAAP. The results of operations for the three and six months ended June 30, 2012 should not be taken as indicative of the results to be expected for the full year.

As used in this document, the terms “we,” “us,” “our” and similar terms refer to the Partnership, unless the context indicates otherwise.

Property and Equipment

During the six months ended June 30, 2011, we received cash of approximately $7.2 million under a state incentive program for jobs creation. This incentive payment, which was determined based on applicable capital expenditures, was accounted for as a refund of sales tax previously paid and reduced the carrying value of our applicable property and equipment.

Note 2—Recent Accounting Pronouncements

Other than as discussed below and in our 2011 Annual Report on Form 10-K, no new accounting pronouncements have become effective during the six months ended June 30, 2012 that are of significance or potential significance to us.

In September 2011, the FASB issued guidance with the purpose of simplifying the goodwill impairment test by permitting entities to perform a qualitative assessment to determine whether further impairment testing is necessary. If qualitative factors indicate that it is more likely than not that the fair value of a reporting unit is greater than its carrying amount, an entity need not perform the two-step goodwill impairment test. This guidance became effective for annual and interim goodwill impairment tests performed for fiscal years beginning after December 15, 2011. We adopted this guidance on January 1, 2012. Our adoption did not have a material impact on our financial position, results of operations or cash flows.

In June 2011, the FASB issued guidance regarding the presentation of other comprehensive income, which was later amended in December 2011, with the purpose of increasing the prominence of other comprehensive income in financial statements. This guidance, as amended, requires entities to present comprehensive income in either (i) a single continuous statement of comprehensive income or (ii) two separate but consecutive statements. This guidance became effective for interim and annual periods beginning after December 15, 2011. We adopted the guidance, as amended, on January 1, 2012. Since this guidance only impacts the presentation of comprehensive income and does not change the composition or calculation of such financial information, adoption did not have a material impact on our financial position, results of operations or cash flows.

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In May 2011, the FASB issued guidance to amend certain fair value measurement and disclosure requirements in an effort to improve consistency with international reporting standards. The amendments generally clarify that the concepts of highest and best use and valuation premise in fair value measurement are relevant only when measuring the fair value of non-financial assets and are not relevant when measuring the fair value of financial assets or of liabilities. In addition, the guidance expanded disclosure requirements associated with (i) unobservable inputs for Level 3 fair value measurements and (ii) items that are not measured at fair value in the financial statements, but for which fair value is required to be disclosed. This guidance became effective prospectively for interim and annual reporting periods beginning after December 15, 2011. We adopted this guidance on January 1, 2012. Other than requiring additional disclosure, which is included in Note 7, our adoption did not have a material impact on our financial position, results of operations or cash flows.

Note 3—Accounts Receivable

We review all outstanding accounts receivable balances on a monthly basis and record a reserve for amounts that we expect will not be fully recovered. We do not apply actual balances against the reserve until we have exhausted substantially all collection efforts. At June 30, 2012 and December 31, 2011, substantially all of our accounts receivable were current and we had no allowance for doubtful accounts.

Our accounts receivable are from a broad mix of customers, including local gas distribution companies, electric utilities, pipelines, direct industrial users, electric power generators, marketers, producers, LNG importers and affiliates of such entities.

To mitigate credit risks related to our accounts receivable, we have in place a rigorous credit review process. We closely monitor market conditions in order to make a determination with respect to the amount, if any, of credit to be extended to any given customer and the form and amount of financial performance assurances we require. Such financial assurances are commonly provided to us in the form of standby letters of credit, parental guarantees or advance cash payments. In addition, we enter into netting arrangements (contractual agreements that allow us and the counterparty to offset receivables and payables against each other) that cover substantially all of our natural gas purchases and sales transactions and also serve to mitigate credit risk.

Note 4—Acquisition

On February 9, 2011, we completed the acquisition of SG Resources Mississippi, L.L.C., owner of the Southern Pines Energy Center natural gas storage facility (the “Southern Pines Acquisition”). The purchase price was approximately $765 million (approximately $750 million net of cash and other working capital acquired).

The purchase price allocation was as follows (in millions):

In conjunction with the Southern Pines Acquisition, we arranged financing totaling approximately $800 million to fund the purchase price, closing costs and the first 18 months of expected expansion capital. The financing consisted of $200 million of borrowings under a promissory note from PAA (see Note 7) and approximately $600 million from the issuance of our common units (see Note 9).

During the six months ended June 30, 2011, we incurred approximately $4.1 million of acquisition-related costs associated with the Southern Pines Acquisition. Such costs are reflected as a component of general and administrative expenses in our condensed consolidated statement of operations.

In May 2011, we entered into an agreement with the former owners of SG Resources Mississippi, LLC with respect to certain outstanding issues and purchase price adjustments as well as the distribution of the remaining purchase price that was escrowed at closing. Pursuant to this agreement, we received approximately $10 million and the balance was remitted to the former owners. Funds received by us have been and will continue to be used to fund anticipated facility development and other related costs identified subsequent to closing. None of these funds were spent during the six months ended June 30, 2012.

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Pro Forma Results

Selected unaudited pro forma results of operations for the six months ended June 30, 2011, assuming the Southern Pines Acquisition had occurred on January 1, 2010, are presented below (in thousands, except per unit amounts):

(1)                  Amount for the period excludes approximately $4.1 million of acquisition costs associated with the Southern Pines Acquisition.

(2)                  Excludes Series B subordinated units. See Note 8, “Net Income per Limited Partner Unit.”

Note 5—Inventory and Base Gas

Inventory and base gas consisted of the following (natural gas volumes in thousands of Mcf and total values in thousands):

(1)                  Total value represents a weighted average associated with various locations; accordingly, these values may not coincide with any published benchmarks for such products.

(2)                  Includes fuel inventory held for operational purposes.

(3)                  As of December 31, 2011, the carrying value of natural gas inventory reflects lower of cost or market adjustments of approximately $6.0 million. No lower of cost or market adjustments were included in the carrying value of natural gas inventory as of June 30, 2012. Lower of cost or market adjustments are reflected as a component of natural gas sales costs in our accompanying condensed consolidated statement of operations. The impacts of such adjustments are generally offset by the recognition of unrealized gains on derivative instruments (see Note 11) being utilized to hedge the future sales of our natural gas inventory.

(4)                  Natural gas inventory balances exclude derivative gains and losses associated with settled derivatives which were entered into to hedge natural gas inventory purchases.  As of June 30, 2012, net deferred losses of approximately $28.3 million associated with settled derivatives are reflected as a component of accumulated other comprehensive income/(loss) in our condensed consolidated balance sheet.  Such amounts will be reclassified to earnings in conjunction with an earnings impact associated with the applicable purchase inventory (typically when such inventory is sold).

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Note 6 — Goodwill

The table below reflects our changes in goodwill for the period indicated (in thousands):

Note 7—Debt

On June 1, 2012, the Partnership and PAA entered into an amendment (the “PAA Promissory Note Amendment”) to the PAA Promissory Note, which was originally entered into during 2011.  The PAA Promissory Note Amendment modified the terms of the PAA Promissory Note by (i) reducing the interest rate from 5.25% per annum to 4.00% per annum and (ii) extending the scheduled maturity date from February 9, 2014 to June 1, 2015. The remaining terms of the PAA Promissory Note were unchanged.

On June 27, 2012 we partially exercised the accordion feature of our revolving credit facility, increasing borrowing capacity from $250 million to $350 million.  Also on June 27, 2012, we reached an agreement with applicable lenders to amend certain terms and provisions of our senior unsecured credit agreement (the “Credit Agreement Amendment”).  Pursuant to the Credit Agreement Amendment, the revolving credit facility commitments may be further increased to $550 million, subject to, among other terms and conditions, obtaining additional or increased lender commitments. The Credit Agreement Amendment also provides for one or more one-year extensions of the maturity date of the revolving credit facility and the date (the “GO Bond Mandatory Put Date”) on which the Purchasers of the GO Bond Term Loans have the right to require the Partnership to repurchase such loans, in each case, subject to applicable lender approval and other terms and conditions set forth in the credit agreement, as amended.  The revolving credit facility will expire and all amounts outstanding under it will mature on August 19, 2016 unless, such maturity date is extended pursuant to the terms of the credit agreement, as amended, and the purchasers of the two GO Bond Term Loans have the right to put, at par, to the Partnership the GO Bond Term Loans on August 19, 2016 unless such GO Bond Mandatory Put Date is extended pursuant to the terms of the credit agreement, as amended. The maturity dates for the GO Bonds, which mature by their terms on May 1, 2032 and August 1, 2035, respectively, were not changed by the Credit Agreement Amendment.   Provisions of the credit agreement providing for the calculation and payment of interest or fees and regarding covenants,  including the financial covenants, events of default and lender remedies were substantially unchanged by the Credit Agreement Amendment, as were the terms  providing for the issuance of letters of credit.

Debt consisted of the following (in thousands):

(1)                  We classify as short-term debt any borrowings under our senior unsecured revolving credit facility that have been designated as working capital borrowings and must be repaid within one year. Such borrowings are primarily related to a portion of our funded hedged natural gas inventory or NYMEX margin requirements. Approximately $0.3 million and $0.5 million of interest expense attributable to such borrowings is reflected as a component of natural gas sales costs in the accompanying condensed consolidated statements of operations for the three and six months ended June 30, 2012, respectively.

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(2)                  We estimate that the fair value of borrowings outstanding under our credit agreement (including the revolving credit facility and GO Bond Term Loans) and the PAA Promissory Note approximate carrying value due to the short maturity of both obligations and the variable interest rate terms set forth under our credit agreement. Our fair value estimate for amounts outstanding under our credit agreement is based upon observable market data and is classified with Level 2 of the fair value hierarchy. With regard to the PAA Promissory Note, our fair valuation estimation process incorporates our estimated credit spread, an unobservable input. As such, we consider this to be a Level 3 measurement within the fair value hierarchy.

Our revolving credit facility includes the ability to issue letters of credit. As of June 30, 2012, we had $3.8 million of outstanding letters of credit under our revolving credit facility.

As of June 30, 2012, we were in compliance with the covenants required by our credit agreement.

Interest payments on the PAA Promissory Note (which commenced on December 31, 2011) are paid semiannually on the last business day of June and December.  Interest paid to PAA during the six months ended June 30, 2012 was approximately $5.0 million. There was no accrued interest payable due under the PAA Promissory Note as of June 30, 2012 or December 31, 2011.

Capitalized interest for the three and six months ended June 30, 2012 was $2.1 million and $4.5 million, respectively, and $3.1 million and $5.7 million for the three and six months ended June 30, 2011, respectively.

Note 8—Net Income per Limited Partner Unit

Basic and diluted net income per limited partner unit is determined pursuant to the two-class method for Master Limited Partnerships as prescribed in the FASB guidance.  The two-class method is an earnings allocation formula that determines earnings to our general partner, limited partner interests and participating securities according to distributions pertaining to the current period’s net income and participation rights in undistributed earnings.  Under this method, all earnings are allocated to our general partner, limited partner interests and participating securities based on their respective rights to receive distributions, regardless of whether those earnings would actually be distributed during a particular period from an economic or practical perspective.  We calculate net income available to limited partners based on the distributions pertaining to the current period’s net income.  After adjusting for the appropriate period’s distributions, the remaining undistributed earnings or excess distributions over earnings, if any, are allocated to the general partner, limited partner interests and participating securities in accordance with the contractual terms of the partnership agreement and as further prescribed under the two-class method.

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The following table sets forth the computation of basic and diluted earnings per limited partner unit for the three and six months ended June 30, 2012 and 2011 (amounts in thousands, except per unit data):

(1)               Participating securities consist of LTIP awards (see Note 10) containing vested distribution equivalent rights which entitle the grantee to a cash payment equal to the cash distribution paid on our outstanding common units.

(2)               For each of the periods presented, our Series B subordinated units were not entitled to participate in our earnings, losses or distributions in accordance with the terms of our partnership agreement as necessary performance conditions have not been satisfied. As a result, no earnings were allocated to the Series B subordinated units in our determination of basic and diluted net income per limited partner unit.

(3)              Substantially all of our LTIP awards (see Note 10), which are classified as equity awards, contain provisions whereby vesting occurs only upon the satisfaction of a performance condition. None of the performance conditions on such awards had been satisfied during any of the periods presented. As such, our outstanding LTIP awards as of June 30, 2012 did not have a material impact in our determination of diluted net income per limited partner unit.

(4)               The conversion of (i) our Series A subordinated units to common units and (ii) our Series B subordinated units to Series A subordinated units or common units is subject to certain performance conditions. None of these performance conditions had been satisfied as of June 30, 2012 therefore, there is no dilutive impact of such units in our determination of diluted net income per limited partner unit.

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Note 9—Partners’ Capital and Distributions

Modification of Terms of Series B Subordinated Units

In February 2012, we modified the terms of the Partnership’s 13.5 million Series B subordinated units, which modification was approved by PAA, the owner of all of the Series B subordinated units. The Partnership’s Series B subordinated units do not participate in quarterly distributions. Instead, the Series B subordinated units convert into Series A subordinated units or common units in five distinct tranches upon the achievement of defined benchmarks tied to the amount of capacity in service at Pine Prairie and increases in our quarterly distributions. The modification increases the quarterly distribution benchmark for the first three of the five tranches, totaling 7.5 million Series B subordinated units in the aggregate, to an annualized level of $1.71 per unit. Previously, the quarterly distribution levels required to cause conversion for these three tranches were at annualized levels of $1.44, $1.53 and $1.63 per unit. The modification, which was made in recognition of the continued challenging market conditions facing the natural gas storage business, benefits our common unitholders by reducing the number of units on which distributions would otherwise be required to be paid in the case of distributions below the annualized level of $1.71. The following table presents the operational and financial benchmarks, as modified, for conversion of the Series B subordinated units into Series A subordinated units for each tranche (units in millions):

(1)               For satisfaction of this benchmark, PNG must, for two consecutive quarters, (i) generate distributable cash flow sufficient to pay a quarterly distribution of at least the annualized distribution benchmark on the weighted average number of common units and Series A subordinated units outstanding during such quarter plus all of such Series B subordinated units and (ii) distribute available cash of at least the annualized distribution benchmark on all outstanding common units and Series A subordinated units and the corresponding distributions on PNG’s general partner’s 2% interest and the related distributions on the incentive distribution rights.  See Note 6 to our consolidated financial statements included in Part IV of our 2011 Annual Report on Form 10-K for a complete discussion of our Series B subordinated units.

Outstanding Units

From December 31, 2011 through June 30, 2012, there were no changes in our issued and outstanding common, Series A subordinated or Series B subordinated units.

Distributions

The following table details the distributions declared for 2012 quarterly periods or paid during the six months ended June 30, 2012 (in millions, except per unit amounts):

(1)                  Payable to unitholders of record on August 3, 2012, for the period April 1, 2012 through June 30, 2012.

Equity Offerings

On February 8, 2011, in connection with the Southern Pines Acquisition, we completed the sale in a private placement of approximately 17.4 million common units to third-party purchasers and approximately 10.2 million common units to PAA for total proceeds of approximately $600 million, including PAA’s proportionate general partner contribution.

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Note 10—Equity Compensation Plans

Long Term Incentive Plan (“LTIP”)

For discussion of our equity compensation awards, see Note 12 to our consolidated financial statements included in Part IV of our 2011 Annual Report on Form 10-K.

In February 2012, the Board of Directors of our general partner approved the modification of certain equity compensation awards previously granted under the 2010 LTIP Plan. As a result of the modification, approximately 232,500 equity-classified phantom unit awards will now vest in the following manner: (i) approximately 70,000 awards, with distribution equivalent rights also modified to begin payment in February 2012, will vest upon the date we pay an annualized distribution of at least $1.45, (ii) approximately 70,000 awards, with distribution equivalent rights also modified to begin payment in May 2013, will vest upon the date we pay an annualized distribution of at least $1.50 and (iii) the remainder, with distribution equivalent rights also modified to begin payment in May 2014, will vest upon the date we pay an annualized distribution of at least $1.55. Fifty percent of any awards that have not vested as of the November 2016 distribution date will vest at that time and the remainder will expire. Additionally, 232,500 of equity-classified phantom unit awards with vesting terms originally tied to the conversion of our Series A and Series B subordinated units were modified such that all these awards will now fully vest upon conversion of the Series A subordinated units to common units. Distribution equivalent rights were also granted with respect to these awards beginning February 2012.

Our equity compensation activity for awards denominated in PNG units is summarized in the following table (units in thousands):