Exhibit 99.1

AMERICAN PACIFIC – News Release

Contact: Dana M. Kelley – (702) 735-2200

E-mail: InvestorRelations@apfc.com

Website: www.apfc.com

AMERICAN PACIFIC REPORTS FISCAL 2013 SECOND QUARTER

RESULTS; INCREASES FULL YEAR GUIDANCE

LAS VEGAS, NEVADA, May 9, 2013 — American Pacific Corporation (NASDAQ: APFC) today reported financial results for its second quarter ended March 31, 2013.

FINANCIAL SUMMARY

Quarter Ended March 31, 2013 Compared to Quarter Ended March 31, 2012

Six Months Ended March 31, 2013 Compared to Six Months Ended March 31, 2012

CONSOLIDATED RESULTS OF OPERATIONS

Revenues – For our Fiscal 2013 second quarter, revenues increased 25% to $50.0 million compared to $39.9 million for the Fiscal 2012 second quarter. For the six months ended March 31, 2013, revenues increased 10% to $86.4 million compared to $78.4 million for the prior year six-month period. The increases are supported by growth from our Fine Chemicals segment, offset partially by the inter-quarter timing of Specialty Chemicals segment revenues. See further discussion below under Segment Highlights.

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Page 1 of Exhibit 99.1

Cost of Revenues and Gross Profit – Fiscal 2013 second quarter cost of revenues was $34.2 million compared to $26.3 million for the Fiscal 2012 second quarter. The Fiscal 2013 second quarter consolidated gross margin decreased to 32% compared to 34% for the Fiscal 2012 second quarter. The Fiscal 2013 six-month period cost of revenues was $55.1 million compared to $52.6 million for the Fiscal 2012 six-month period. The Fiscal 2013 six-month period consolidated gross margin was 36% compared to 33% for the Fiscal 2012 six-month period. Fine Chemicals segment gross margin improved significantly in each of the Fiscal 2013 periods. However, for the Fiscal 2013 second quarter, Fine Chemicals comprised a larger percentage of our consolidated business which resulted in the consolidated gross margin decline. On a consolidated level, one of the most significant factors that affects, and should continue to affect, the comparison of our consolidated gross profit and gross margin from period to period is the change in revenue mix among our segments. The revenue contribution by each of our segments is indicated in the following table.

See further discussion of gross profit and gross margin at the segment levels under the heading Segment Highlights.

Operating Expenses – For our Fiscal 2013 second quarter, operating expenses were $11.0 million compared to $8.8 million for the Fiscal 2012 second quarter. For our Fiscal 2013 six-month period, operating expenses were $21.5 million compared to $18.3 million for the Fiscal 2012 six-month period. The most significant components of the six-month period increase were approximately $2.2 million for accrued incentive compensation, approximately $0.6 million for increased costs from our defined benefit retirement plans, and approximately $0.3 million for corporate shareholder matters. The increase in incentive compensation occurred primarily due to the timing of incentive compensation accruals. Strong operating performance in the first half of Fiscal 2013 has resulted in incentive-based compensation costs of approximately $1.6 million being recorded earlier in this fiscal year than in the prior fiscal year.

SEGMENT HIGHLIGHTS

Fine Chemicals Segment

Our Fine Chemicals segment reflects the operating results of our wholly-owned subsidiaries Ampac Fine Chemicals LLC and AMPAC Fine Chemicals Texas, LLC (collectively, “AFC”).

Quarter Ended March 31, 2013 Compared to Quarter Ended March 31, 2012

Six Months Ended March 31, 2013 Compared to Six Months Ended March 31, 2012

Fine Chemicals segment revenues increased 81% and 39% for the Fiscal 2013 second quarter and six-month period, respectively, each compared to the corresponding Fiscal 2012 periods. Oncology product revenues increased in both the Fiscal 2013 second quarter and the six-month period, supported by revenues from new oncology products for drugs that were commercialized in the later part of Fiscal 2012. The Fiscal 2013 second quarter also includes increases from the anti-viral, central nervous systems and development product groups. These increases are substantially due to inter-quarter timing when compared to the prior fiscal year.

The Fine Chemicals segment reported operating income of $3.8 million for the Fiscal 2013 second quarter compared to an operating loss of $1.0 million for the Fiscal 2012 second quarter. The improvement includes a ten percentage point increase in gross margin, offset partially by increased operating expenses. Fine Chemicals segment operating income for the Fiscal 2013 six-month period was

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$5.0 million compared to a loss of $2.2 million for the six-month period in the prior fiscal year. For the Fiscal 2013 six-month period, the gross margin percentage increased twelve percentage points. Gross margin improvements reflect significant improvements in manufacturing operations, as well as better contractual pricing on certain core products. Our Fine Chemicals segment has dedicated significant efforts over the last two fiscal years to improving the efficiency of its manufacturing activities. Redesigned key processes continued to yield targeted throughput ranges during the Fiscal 2013 periods. In contrast, during the Fiscal 2012 periods, the Fine Chemicals segment had not yet achieved the benefits of these improvements.

Fine Chemicals operating expenses increased in the Fiscal 2013 periods primarily due to the timing of incentive compensation accruals. Strong operating performance in the first half of Fiscal 2013 has resulted in incentive-based compensation costs being recorded earlier in this fiscal year than in the prior fiscal year.

Specialty Chemicals Segment

Our Specialty Chemicals segment revenues include the operating results from our perchlorate, sodium azide and Halotron product lines, with our perchlorate product lines comprising 83% and 87% of Specialty Chemicals segment revenues in the Fiscal 2013 and 2012 six-month periods, respectively.

Quarter Ended March 31, 2013 Compared to Quarter Ended March 31, 2012

Six Months Ended March 31, 2013 Compared to Six Months Ended March 31, 2012

Specialty Chemicals segment revenues of $11.9 million for the Fiscal 2013 second quarter and $26.3 million for the Fiscal 2013 six-month period, reflect decreases of 37% and 21%, respectively, as compared to the prior fiscal year periods. The revenue variances reflect changes in inter-quarter timing of perchlorate volume. We anticipate that Specialty Chemicals segment revenues variances will reverse in the second half of Fiscal 2013.

The variance in Specialty Chemicals segment revenues reflects the following factors:

The average price per pound of perchlorates decreased in the Fiscal 2013 second quarter because lower-priced, non rocket-grade perchlorate accounted for a larger percentage of the total perchlorate volume. Fiscal 2013 volume was predominately strategic and tactical missile programs. Both space programs and tactical missile programs had strong volume during the Fiscal 2012 periods.

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The decreases in Specialty Chemicals segment operating income for the Fiscal 2013 periods are consistent with the associated revenue decreases. As a percentage of revenues, operating margins declined to 44% in the Fiscal 2013 second quarter and declined to 50% in the Fiscal 2013 six-month period, compared to 49% and 51%, respectively, for the corresponding prior fiscal year periods. The decreases occurred because the lower volume provided less gross profit to offset the consistent general and administrative expenses. Specialty Chemicals segment gross margins were consistent for the periods presented.

CAPITAL AND LIQUIDITY HIGHLIGHTS

Liquidity – As of March 31, 2013, we had cash balances of $26.7 million and no borrowings against our revolving credit facility.

Operating Cash Flows – Operating activities provided cash of $8.6 million for the Fiscal 2013 six-month period compared to a use of cash of $6.8 million for the prior fiscal year six-month period, an improvement of $15.4 million.

Significant components of the change in cash flow from operating activities include:

The improvement in working capital cash flow reflects additional customer deposits received by our Specialty Chemicals segment in the Fiscal 2013 second quarter.

Cash paid for income taxes increased because our federal operating loss carryforwards were fully utilized in Fiscal 2012. Accordingly, we expect to pay cash taxes in Fiscal 2013.

Cash paid for interest in the Fiscal 2013 six-month period decreased as compared to the Fiscal 2012 six-month period reflecting both lower outstanding debt balances and lower interest rates that resulted from our refinancing in October 2012. Also in connection with the October 2012 refinancing, we incurred cash redemption costs of approximately $1.6 million comprised primarily of the call premium to redeem the senior notes.

We make payments to fund defined benefit pension obligations at a level of at least 80% of the obligation. Our contributions were reduced in the Fiscal 2013 six-month period, as compared to the Fiscal 2012 six-month period, primarily due to improved plan asset returns in Fiscal 2012. In Fiscal 2012, we made additional contributions to our pension plans because the return on pension plan assets in the preceding year was not sufficient to maintain our target funding requirements.

Investing Cash Flows – Capital expenditures in the Fiscal 2013 six-month period were $5.9 million compared to $2.4 million for the Fiscal 2012 six-month period. The increase primarily relates to Fiscal 2013 projects that will provide additional mid-scale capacity for our Fine Chemicals segment.

Financing Cash Flows – For our Fiscal 2013 six-month period financing activities used cash of $7.2 million compared to a use of cash of $0.04 million for the Fiscal 2012 six-month period. The Fiscal 2013 six-month period amount includes a reduction in our long-term debt of $5.0 million and debt issuance

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costs of approximately $1.4 million, each incurred in connection with our October 2012 refinancing activities. Subsequent to our October 2012 refinancing, we also made scheduled principal payments for our new term loan in the amount of $2.3 million.

OUTLOOK

Based on our performance this fiscal year to date, which includes existing backlog, anticipated orders and manufacturing efficiencies that are improved from our prior expectations, we are increasing our guidance for Fiscal 2013. We expect consolidated revenues of at least $205.0 million and Adjusted EBITDA of at least $47.0 million. We are anticipating our capital expenditures, which do not include environmental remediation spending, for Fiscal 2013 to be approximately $14.0 million.

Our Fiscal 2013 guidance for Adjusted EBITDA is computed by adding estimated amounts for depreciation and amortization of $13.5 million, interest expense and refinancing costs of $5.8 million, share-based compensation expense and other items of $1.0 million and income taxes of $9.5 million to estimated net income of $17.2 million.

NON-GAAP FINANCIAL INFORMATION AND BASIS OF PRESENTATION

We have provided non-GAAP measures as a supplement to financial results based on GAAP. A reconciliation of the non-GAAP measures to the most directly comparable GAAP measures is included in the accompanying supplemental data. Segment EBITDA is defined as segment operating income (loss) plus depreciation and amortization. Adjusted EBITDA is defined as income (loss) from continuing operations before income tax expense (benefit), interest expense, loss on debt extinguishment, depreciation and amortization, share-based compensation and environmental remediation charges (if any).

Segment EBITDA and Adjusted EBITDA are not financial measures calculated in accordance with GAAP and should not be considered as an alternative to income (loss) from continuing operations as performance measures. Each EBITDA measure is presented solely as a supplemental disclosure because management believes that each is a useful performance measure that is widely used within the industries in which we operate. In addition, EBITDA measures are significant measurements for covenant compliance under our credit facility. Each EBITDA measure is not calculated in the same manner by all companies and, accordingly, may not be an appropriate measure for comparison.

Revenues and expenses associated with our former Aerospace Equipment segment operations, which were divested effective August 1, 2012, are presented as discontinued operations for all periods presented.

We report our results based on a fiscal year which ends on September 30. References to Fiscal years refer to the twelve months ended or ending September 30 of the Fiscal year referenced.

INVESTOR TELECONFERENCE

We invite you to participate in a teleconference with our executive management covering our Fiscal 2013 second quarter financial results. The investor teleconference will be held Thursday, May 9, 2013, at 1:30 p.m., Pacific Standard Time. The teleconference will include a presentation by management followed by a question and answer session. The teleconference can be accessed by dialing 877-261-8990 between 1:15 and 1:30 p.m., Pacific Standard Time. Please reference passcode #34802475. As is our customary practice, a live webcast of the teleconference is being provided by Thomson Reuters. Links to the webcast and the earnings release are available in the Investors section of our website at www.apfc.com, and will be available for replay until a few days before our next quarterly investor teleconference.

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RISK FACTORS/FORWARD-LOOKING STATEMENTS

The unaudited financial results included in this release are preliminary. Statements contained in this earnings release that are not purely historical are forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995, Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934, including without limitation the statement regarding the impact that change in revenue mix among our segments will have on comparisons of our consolidated gross profit and gross margin in the future, statements regarding our expectations for product revenues, sales volumes, working capital, interest expense, tax obligations, and capital expenditures, statements regarding the impact of process improvements and other efficiency and cost savings initiatives, statements regarding the expected impact of the timing of orders, sales and production activities on quarterly revenues, statements regarding the expected benefit of our credit swap agreement, statements regarding the impact that principal payments under our Credit Facility will have on our liquidity, statements regarding our ability to focus on the growth and performance of our pharmaceutical-related product lines following the sale of our Aerospace Equipment segment and the statements in the “Outlook” section of this earnings release. Words such as “expect”, “anticipate”, “should”, “future” and similar expressions are intended to identify forward-looking statements. The inclusion of forward-looking statements should not be regarded as a representation by us that any of our expectations will be achieved. Actual results may differ materially from future results or outcomes expressed or implied by forward-looking statements set forth in the release due to risks, uncertainties and other important factors inherent in our business. Factors that might cause actual results to differ include, but are not limited to, the actual placement, timing and delivery of orders for new and/or existing products as well as the following:

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Readers of this earnings release are referred to our Annual Report on Form 10-K for Fiscal 2012 and our other filings with the Securities and Exchange Commission for further discussion of these and other factors that could affect our future results. The forward-looking statements contained in this earnings release are made as of the date hereof, and we assume no obligation to update for actual results or to update the reasons why actual results could differ materially from those projected in the forward-looking statements, except as required by law. In addition, the operating results for the quarter and six months ended March 31, 2013 and cash flows for the six months ended March 31, 2013 are not necessarily indicative of the results that will be achieved for future periods.

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ABOUT AMERICAN PACIFIC CORPORATION

American Pacific Corporation (AMPAC) is a leading custom manufacturer of fine chemicals and specialty chemicals within its focused markets. We supply active pharmaceutical ingredients and advanced intermediates to the pharmaceutical industry. For the aerospace and defense industry we provide specialty chemicals used in solid rocket motors for space launch and military missiles. We produce clean agent chemicals for the fire protection industry, as well as electro-chemical equipment for the water treatment industry. Our products are designed to meet customer specifications and often must meet certain governmental and regulatory approvals. Additional information about us can be obtained by visiting our web site at www.apfc.com.

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AMERICAN PACIFIC CORPORATION

Condensed Consolidated Statements of Operations

(Unaudited, Dollars in Thousands, Except per Share Amounts)

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AMERICAN PACIFIC CORPORATION

Condensed Consolidated Balance Sheets

(Unaudited, Dollars in Thousands, Except per Share Amounts)

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AMERICAN PACIFIC CORPORATION

Condensed Consolidated Statements of Cash Flows

(Unaudited, Dollars in Thousands)

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AMERICAN PACIFIC CORPORATION

Supplemental Data

(Unaudited, Dollars in Thousands)

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