Exhibit 99.1

Oasis Petroleum Inc. Announces Quarter Ending March 31, 2013 Earnings

Houston, Texas — May 7, 2013 — Oasis Petroleum Inc. (NYSE: OAS) (“Oasis” or the “Company”) today announced financial results for the quarter ended March 31, 2013.

Highlights for the first quarter of 2013 include:

“The momentum of our operational success continued into the first quarter, as we again exceeded our production guidance and drove down our average capital cost per well by 5% to $8.4 million, excluding the impact of Oasis Well Services (“OWS”),” said Thomas B. Nusz, Oasis’ Chairman and Chief Executive Officer. “OWS remains a key value driver for Oasis on numerous fronts, including driving down well costs and increasing the efficiency and quality of our fracs. OWS reduced overall capital expenditures (“CapEx”) for the Company by $8.1 million in the first quarter of 2013, which equates to $0.3 million per net operated well completed in the first quarter.”

Mr. Nusz added, “Our drilling and completions teams performed extremely well through tough winter conditions and our production team continues to do a great job minimizing downtime on our operated wells. The land team increased our working interest in operated wells, and our lower well costs offset the additional capital costs associated with the increase in net completions relative to our original plan, leaving our drilling and completion capital in the first quarter in line with our plan. We expect that the pace of gross operated completions will decline to 18 to 20 wells during the second quarter of 2013, as we manage the logistics of pad drilling operations and spring break-up. Along with that, we expect volumes in the second quarter to be relatively flat compared to the first quarter, and we currently expect second quarter production to range between 29,000 Boepd and 31,000 Boepd. Additionally, we are increasing our full-year guidance to 31,000 Boepd to 34,000 Boepd.”

Formation of Oasis Midstream Services

In the first quarter of 2013, Oasis formed OMS and transferred its SWD and other midstream assets to OMS. OMS provides midstream services to the Company and will provide Oasis with future optionality, as utilization of these assets continues to grow.

With the formation of OMS, the Company made the appropriate prospective changes to the presentation of financial statements. Therefore, the consolidated statement of operations now has revenue and operating expenses for OMS, which are related to the revenue and operating expenses for third-party working interest owners’ volumes in the Company’s operated wells. Historically, revenue from third parties was an offset to lease operating expenses (“LOE”), and it is now included within well services and

midstream revenues. Additionally, the portion of the Company’s general and administrative (“G&A”) expenses, operating expenses and depreciation that is associated with operated volumes is now charged to LOE. The directional impact of OMS on the consolidated statement of operations is as follows:

Oasis is updating its outlook for 2013, see “Updated Outlook for 2013” below, due to the formation of OMS and its updated expectations for the year.

Operational and Financial Update

Average daily production by project area is listed in the following table:

The following table describes the Company’s producing wells by project area in the Williston Basin as of March 31, 2013:

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Additionally, the Company also has a backlog of gross operated wells waiting on completion (“WOC”) and wells that were drilling as of March 31, 2013, as shown below:

The Company’s average price per barrel of oil, without realized derivatives, was $93.33 in the first quarter of 2013, compared to $88.10 in the first quarter of 2012 and $86.82 in the fourth quarter of 2012. The Company’s average price differential compared to NYMEX West Texas Intermediate (“WTI”) crude oil index prices was 1% in the first quarter of 2013, compared to 14% in the first quarter of 2012 and 2% in the fourth quarter of 2012. The Company’s differentials continued to improve in the fourth quarter of 2012 and the first quarter of 2013 compared to the first quarter of 2012 due to transportation capacity additions in the Williston Basin outpacing production growth along with increased connections to third party oil gathering systems, which provide flexibility with access to numerous rail and pipeline delivery points, and fewer refinery constraints.

Revenues are detailed in the following table:

Operating expenses are detailed in the following table:

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The sequential quarter-over-quarter increase in LOE per BOE was primarily due to the formation of OMS in the first quarter of 2013. Excluding the impact of OMS, LOE would have been $6.58 per Boe in the first quarter of 2013 compared to $6.68 per Boe in the fourth quarter of 2012. The Company is increasing its overall LOE guidance range for the full year 2013 by $0.50 per Boe to $6.25 to $7.50 per Boe to account for the formation of OMS.

The increase in marketing, transportation, and gathering expenses from the fourth quarter of 2012 to the first quarter of 2013 is due to higher operated volumes flowing through third party oil gathering pipelines in the first quarter of 2013. Currently, the Company is flowing approximately 85% of its gross operated oil production through these gathering systems. While transporting volumes through third party oil gathering pipelines increases marketing, transportation and gathering expenses, it improves oil price realizations by reducing trucking costs, which are reflected in the oil price differential, rather than as an expense.

Production taxes as a percentage of oil and gas revenues were 9.1% in the first quarter of 2013, 9.6% in the first quarter of 2012 and 9.4% in the fourth quarter of 2012. The Company’s production tax rate decreased in the first quarter of 2013, primarily as a result of additional new Montana wells subject to lower incentivized production tax rates.

Depreciation, depletion and amortization expenses (“DD&A”) totaled $66.3 million in the first quarter of 2013, $38.9 million in the first quarter of 2012 and $66.0 million in the fourth quarter of 2012. DD&A was $24.42 per Boe in the first quarter of 2013, $24.23 per Boe in the first quarter of 2012 and $26.01 per Boe in the fourth quarter of 2012. The decrease in DD&A of $1.59 per Boe in the first quarter of 2013 over the fourth quarter of 2012 was primarily a result of the increase in reserves, lower well costs, and the impact of OMS.

G&A expenses totaled $13.9 million in the first quarter of 2013, $12.2 million in the first quarter of 2012 and $17.6 million in the fourth quarter of 2012. The overall decrease in G&A expenses from the fourth quarter of 2012 to the first quarter of 2013 was primarily due to higher performance related compensation expenses in the fourth quarter of 2012. G&A expenses were $5.10 per Boe in the first quarter of 2013, $7.60 per Boe in the first quarter of 2012 and $6.93 per Boe in the fourth quarter of 2012. Amortization of stock-based compensation, which is included in the aggregate G&A expenses, was $2.3 million, or $0.84 per Boe, in the first quarter of 2013 as compared to $1.6 million, or $0.99 per Boe, in the first quarter of 2012 and $3.7 million, or $1.46 per Boe, in the fourth quarter of 2012.

The Company’s derivative activities are detailed in the following table:

The Company recorded non-cash charges for the impairment of oil and natural gas properties of $0.5 million in the first quarter of 2013 related to unproved property leases that expired or have been forecasted to expire under current drilling plans, as compared to $0.4 million in the first quarter of 2012 and $1.0 million in the fourth quarter of 2012.

Interest expense increased $7.3 million to $21.2 million for the first quarter of 2013 compared to the first quarter of 2012 and decreased $8 thousand compared to the fourth quarter of 2012. The $7.3 million increase was the result of additional interest expense from the Company’s issuance of 6.875% senior unsecured notes in July 2012. Capitalized interest totaled $0.8 million for the first quarter of 2013 and for both the first and fourth quarters of 2012.

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Income tax expense was $31.1 million for the three months ended March 31, 2013, resulting in an effective tax rate of 37.5%. The Company’s income tax expense for the three months ended March 31, 2012 was recorded at 37.4% of pre-tax net income. The Company’s effective tax rate is expected to continue to closely approximate the statutory rate applicable to the U.S. and the blended state rate of the states in which the Company conducts business.

Adjusted EBITDA for the first quarter of 2013 was $191.4 million, an increase of $90.2 million, or 89%, over the first quarter of 2012 of $101.1 million, and a 17% increase over the fourth quarter of 2012 of $163.5 million. For a definition of Adjusted EBITDA and a reconciliation of Adjusted EBITDA to net income and net cash provided by operating activities, see “Non-GAAP Financial Measures” below.

For the first quarter of 2013, the Company reported net income of $51.9 million, or $0.56 per diluted share, as compared to net income of $16.4 million, or $0.18 per diluted share, for the first quarter of 2012. The Company’s first quarter 2013 results were impacted by several non-cash items, including a $16.3 million unrealized loss on derivative instruments and a $0.5 million impairment of oil and gas properties. Excluding these items and their tax effect, the first quarter 2013 Adjusted Net Income (non-GAAP) was $62.4 million, or $0.67 per diluted share. Excluding similar non-cash items and their tax effect, Adjusted Net Income (non-GAAP) for the first quarter of 2012 was $27.5 million, or $0.30 per diluted share. For a definition of Adjusted Net Income and a reconciliation of net income to Adjusted Net Income, see “Non-GAAP Financial Measures” below.

Updated Outlook for 2013

The following table provides an update to Oasis’ forward-looking guidance for 2013:

Additionally, the Company expects OMS revenues to continue to grow moderately in 2013, as more operated wells are connected to the gathering system and more salt water is disposed in its disposal wells. Oasis anticipates OMS operating expenses to grow in relative proportion to OMS revenues throughout 2013. Oasis budgeted $43 million for infrastructure related CapEx, which is now related to OMS expenditures for the year.

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CapEx

The following table depicts the Company’s E&P CapEx by project area and total CapEx by category:

Liquidity

On March 31, 2013, Oasis had total cash and cash equivalents of $166.0 million and short-term investments of $25.9 million. As of March 31, 2013, the Company had no outstanding indebtedness and $2.2 million of outstanding letters of credit issued under its revolving credit facility, resulting in an unused borrowing base capacity of $747.8 million. On April 5, 2013, the Company entered into a second amended and restated credit agreement (the “Second Amended Credit Facility”) and completed its semi-annual redetermination of the Company’s borrowing base. Pursuant to the Second Amended Credit Facility, the Company’s borrowing base increased from $750 million to $1,250 million. However, the Company elected to limit the lenders’ aggregate commitment to $900 million. The lenders’ aggregate commitment can be increased to the full $1,250 million borrowing base by increasing the commitment of one or more lenders.

Hedging Activity

As of May 7, 2013, the Company had the following outstanding commodity derivative contracts, all of which are priced off of WTI and settle monthly:

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Conference Call Information

Investors, analysts and other interested parties are invited to listen to the conference call:

A recording of the conference call will be available beginning at 1:00 p.m. Central Time on the day of the call and will be available until Wednesday, May 15, 2013 by dialing:

The conference call will also be available for replay at www.oasispetroleum.com.

Forward-Looking Statements

This press release contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. All statements, other than statements of historical facts, included in this press release that address activities, events or developments that the Company expects, believes or anticipates will or may occur in the future are forward-looking statements. Without limiting the generality of the foregoing, forward-looking statements contained in this press release specifically include the expectations of plans, strategies, objectives and anticipated financial and operating results of the Company, including the Company’s drilling program, production, derivative instruments, capital expenditure levels and other guidance included in this press release. These statements are based on certain assumptions made by the Company based on management’s experience and perception of historical trends, current conditions, anticipated future developments and other factors believed to be appropriate. Such statements are subject to a number of assumptions, risks and uncertainties, many of which are beyond the control of the Company, which may cause actual results to differ materially from those implied or expressed by the forward-looking statements. These include, but

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are not limited to, changes in oil and natural gas prices, weather and environmental conditions, the timing of planned capital expenditures, availability of acquisitions, uncertainties in estimating proved reserves and forecasting production results, operational factors affecting the commencement or maintenance of producing wells, the condition of the capital markets generally, as well as the Company’s ability to access them, the proximity to and capacity of transportation facilities, and uncertainties regarding environmental regulations or litigation and other legal or regulatory developments affecting the Company’s business and other important factors that could cause actual results to differ materially from those projected as described in the Company’s reports filed with the SEC.

Any forward-looking statement speaks only as of the date on which such statement is made and the Company undertakes no obligation to correct or update any forward-looking statement, whether as a result of new information, future events or otherwise, except as required by applicable law.

About Oasis Petroleum Inc.

Oasis is an independent exploration and production company focused on the acquisition and development of unconventional oil and natural gas resources, primarily operating in the Williston Basin. For more information, please visit the Company’s website at www.oasispetroleum.com.

Contact:

Oasis Petroleum Inc.

Richard Robuck, (281) 404-9600

Director – Finance

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Oasis Petroleum Inc. Financial Statements

Oasis Petroleum Inc.

Condensed Consolidated Balance Sheet

(Unaudited)

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Oasis Petroleum Inc.

Condensed Consolidated Statement of Operations

(Unaudited)

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Oasis Petroleum Inc.

Selected Financial and Operational Statistics

(Unaudited)

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Oasis Petroleum Inc.

Condensed Consolidated Statement of Cash Flows

(Unaudited)

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Non-GAAP Financial Measures

Adjusted EBITDA is a supplemental non-GAAP financial measure that is used by management and external users of the Company’s consolidated financial statements, such as industry analysts, investors, lenders and rating agencies. The Company defines Adjusted EBITDA as earnings before interest expense, income taxes, depreciation, depletion, amortization, exploration expenses and other similar non-cash charges. Adjusted EBITDA is not a measure of net income or cash flows as determined by United States generally accepted accounting principles, or GAAP.

The following tables present a reconciliation of the non-GAAP financial measure of Adjusted EBITDA to the GAAP financial measures of net income and net cash provided by operating activities, respectively.