Whiting Petroleum : WLL / OAS Merger Presentation

Whiting & Oasis

Strategic Merger Of Equals

March 7, 2022

Important Disclosures

No Offer or Solicitation

Communications in this investor presentation do not constitute an offer to sell or the solicitation of an offer to subscribe for or buy any securities or a solicitation of any vote or approval with respect to the proposed transaction or otherwise, nor shall there be any sale, issuance or transfer of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction.

Additional Information and Where You Can Find It

In connection with the proposed transaction, Whiting Petroleum Corporation ("Whiting") and Oasis Petroleum Inc. ("Oasis") intend to file materials with the Securities and Exchange Commission ("SEC"), including a Registration Statement on Form S-4 of Oasis (the "Registration Statement") that will include a joint proxy statement/prospectus of Whiting and Oasis. After the Registration Statement is declared effective by the SEC, Whiting and Oasis intend to mail a definitive joint proxy statement/prospectus to the shareholders of Oasis and the shareholders of Whiting. This investor presentation is not a substitute for the joint proxy statement/prospectus or the Registration Statement or for any other document that Oasis or Whiting may file with the SEC and send to Oasis' shareholders and/or Whiting's shareholders in connection with the proposed transaction. INVESTORS AND SECURITY HOLDERS OF OASIS AND

WHIITING ARE URGED TO CAREFULLY AND THOROUGHLY READ THE JOINT PROXY STATEMENT/PROSPECTUS AND THE REGISTRATION STATEMENT, AS EACH MAY BE AMENDED OR SUPPLEMENTED FROM TIME TO TIME, AND OTHER RELEVANT DOCUMENTS FILED BY WHITING AND OASIS WITH THE SEC, WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT WHITING, OASIS, THE PROPOSED TRANSACTION, THE RISKS RELATED THERETO AND RELATED MATTERS.

Investors will be able to obtain free copies of the Registration Statement and joint proxy statement/prospectus, as each may be amended from time to time, and other relevant documents filed by Whiting and Oasis with the SEC (when they become available) through the website maintained by the SEC at www.sec.gov. Copies of documents filed with the SEC by Whiting will be available free of charge from Whiting's website at www.whiting.com under the "Investor

Relations" tab or by contacting Whiting's Investor Relations Department at [phone] or [e-mail]. Copies of documents filed with the SEC by Oasis will be available free of charge from Oasis' website at www.oasispetroleum.com under the "Investor Relations" tab or by contacting Oasis' Investor Relations Department at [phone] or [e-mail].

Participants in the Solicitation

Whiting, Oasis and their respective directors and certain of their executive officers and other members of management and employees may be deemed, under SEC rules, to be participants in the solicitation of proxies from Oasis' shareholders and Whiting's shareholders in connection with the transaction. Information regarding the executive officers and directors of Oasis is included in its definitive proxy statement for its 2021 annual meeting filed with the SEC on March 18, 2021. Information regarding the executive officers and directors of Whiting is included in its definitive proxy statement for its 2021 annual meeting filed with the SEC on March 29, 2021. Additional information regarding the persons who may be deemed participants and their direct and indirect interests, by security holdings or otherwise, will be set forth in the Registration Statement, joint proxy statement/prospectus and other materials when they are filed with the SEC in connection with the transaction. Free copies of these documents may be obtained as described in the paragraphs above.

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Cautionary Statement Regarding Forward-Looking Statements

Forward-Looking Statements

Certain statements in this document concerning the transaction, including any statements regarding the expected timetable for completing the transaction, the results, effects, benefits and synergies of the transaction, future opportunities for the combined company, future financial performance and condition, guidance and any other statements regarding Whiting's or Oasis' future expectations, beliefs, plans, objectives, financial conditions, assumptions or future events or performance that are not historical facts are "forward- looking" statements based on assumptions currently believed to be valid. Forward-looking statements are all statements other than statements of historical facts. The words "anticipate," "believe," "ensure," "expect," "if," "intend," "estimate," "probable," "project," "forecasts," "predict," "outlook," "aim," "will," "could," "should," "would," "potential," "may," "might," "anticipate," "likely" "plan," "positioned," "strategy," and similar expressions or other words of similar meaning, and the negatives thereof, are intended to identify forward-looking statements. Specific forward-looking statements include statements regarding Whiting's and Oasis' plans and expectations with respect to the transaction and the anticipated impact of the transaction on the combined company's results of

operations, financial position, growth opportunities and competitive position. The forward-looking statements are intended to be subject to the safe harbor provided by Section 27A of the Securities Act of 1933, Section 21E of the Securities Exchange Act of 1934 and the Private Securities Litigation Reform Act of 1995.

These forward-looking statements involve significant risks and uncertainties that could cause actual results to differ materially from those anticipated, including, but not limited to, the possibility that shareholders of Oasis may not approve the issuance of new shares of Oasis common stock in the transaction or that shareholders of Whiting may not approve the merger agreement; the risk that a condition to closing of the transaction may not be satisfied, that either party may terminate the merger agreement or that the closing of the transaction might be delayed or not occur at all; potential adverse reactions or changes to business or employee relationships, including those resulting from the announcement or completion of the transaction; the diversion of management time on transaction- related issues; the ultimate timing, outcome and results of integrating the operations of Whiting and Oasis; the effects of the business combination of Whiting and Oasis, including the combined company's future financial condition, results of operations, strategy and plans; the ability of the combined company to realize anticipated synergies in the timeframe expected or at all; changes in capital markets and the ability of the combined company to finance operations in the manner expected; regulatory approval of the transaction; the effects of commodity prices; the risks of oil and gas activities; and the fact that operating costs and business disruption may be greater than expected following the public announcement or consummation of the transaction. Expectations regarding business outlook, including changes in revenue, pricing, capital expenditures, cash flow generation, strategies for the combined company's operations, oil and natural gas market conditions, legal, economic and regulatory conditions, and environmental matters are only forecasts regarding these matters.

Additional factors that could cause results to differ materially from those described above can be found in Whiting's Annual Report on Form 10-K for the year ended December 31, 2021 (as amended), which is on file with the SEC and available from Whiting's website at www.whiting.com under the "Investor Relations" tab, and in other documents Whiting files with the SEC and in Oasis' Annual Report on Form 10-K for the year ended December 31, 2021, which is on file with the SEC and available from Oasis' website at www.oasispetroleum.com under the "Investor Relations" tab, and in other documents Oasis files with the SEC.

All forward-looking statements speak only as of the date they are made and are based on information available at that time. Neither Whiting nor Oasis assumes any obligation to update forward-looking statements to reflect circumstances or events that occur after the date the forward-looking statements were made or to reflect the occurrence of unanticipated events except as required by federal securities laws. As forward-looking statements involve significant risks and uncertainties, caution should be exercised against placing undue reliance on such statements.

Non-GAAP Financial Measures

EBITDAX and free cash flow are supplemental financial measures that are not presented in accordance with generally accepted accounting principles in the United States ("GAAP"). These non-GAAP measure should not be considered in isolation or as a substitute for net income (loss), operating income (loss), net cash provided by (used in) operating activities, earnings (loss) per share or any other measures prepared under GAAP. Because these non-GAAP measures exclude some but not all items that affect net income (loss) and may vary among companies, the amounts presented may not be comparable to similar metrics of other companies. Reconciliations of these non-GAAP financial measures to their most comparable GAAP measure can be found in the annual report on Form 10-K, quarterly reports on Form 10-Q and Whiting's and Oasis' website at www.whiting,com and www.oasispetroleum.com. Amounts excluded from these non-GAAP measure in future periods could be significant.

Cautionary Statement Regarding Oil and Gas Quantities

The SEC requires oil and gas companies, in their filings with the SEC, to disclose proved reserves, which are those quantities of oil and gas, which, by analysis of geoscience and engineering data, can be estimated with reasonable certainty to be economically producible-from a given date forward, from known reservoirs, and under existing economic conditions (using unweighted average 12-month first day of the month prices), operating methods, and government regulations-prior to the time at which contracts providing the right to operate expire, unless evidence indicates that renewal is reasonably certain, regardless of whether deterministic or probabilistic methods are used for the estimation. The accuracy of any reserve estimate depends on the quality of available data, the interpretation of such data and price and cost assumptions made by reserve engineers. In addition, the results of drilling, testing and production activities of the exploration and development companies may justify revisions of estimates that were made previously. If significant, such revisions could impact Whiting's and Oasis' strategy and future prospects. Accordingly, reserve estimates may differ significantly from the quantities of oil and natural gas that are ultimately recovered. The SEC also permits the disclosure of separate estimates of probable or possible reserves that meet SEC definitions for such reserves; however, neither Whiting nor Oasis currently discloses probable or possible reserves in its SEC filings.

The production forecasts and expectations of the combined company for future periods are dependent upon many assumptions, including estimates of production decline rates from existing wells and the undertaking and outcome of future drilling activity, which may be affected by significant commodity price declines or drilling cost increases.

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Combined Company Will Be a

Premier Williston Basin Company

		•	~$6B equity value
✓	Materially Enhanced	•	167.8 Mboe/d 4Q21 net production (3-stream)1
Scale	•	97.3 Mbo/d 4Q21 net production
		•	972k net acres
	High-Quality Assets	•	~$1.2B FCF for full year 2022E4
✓	Generate Significant,
•	Combined inventory supports ~10 years of development
Sustainable
	Free Cash Flow		at pro forma 2022E pace5
	Shareholder	•<40% 2022 expected re-investment rate 4, maintaining
✓		~flat production
Returns-Focused	•	2H22 return of capital targeted at 60% of FCF
	Business Model	• Combined board to determine go forward plan
		• ~0.2x net debt / 1H22E annualized EBITDAX4 at close
✓	Maintains Financial	•	Strong liquidity with minimal borrowings5 under $900MM
Strength / Flexibility		borrowing base6 as close
		• No near-term maturities
✓
ESG Leadership	• Continued commitment to ESG, sustainability and
	capitalizing on combined best practices

972k	167.8	92%	68%
NET ACRES	Mboepd1	OPERATED2	WORKING INTEREST3

OAS

WLL

1)	Converted to 3 stream for Oasis for 4Q21	4)	Pro forma combined company run at $85 WTI and $3.50 HH at approximately midpoint of guidance. Reinvestment rate is before dividends.	4
2)	Operated based on 2021 combined PDP reserves	5)	Economic locations (>30% IRR @ $60/Bbl WTI flat) and assuming 108 - 110 2022E TILs
3)	Working interest of expected PF wells completed in 2022	6)	Includes Oasis' borrowing base. Oasis' current elected commitments total $450MM.

Transaction Overview

	Transaction	• 0.5774 OAS shares and $6.25 of cash per WLL share
	•	Special dividend of $15.00 per share to OAS shareholders at close
	Structure
	•	Pro forma equity ownership: 53% WLL and 47% OAS1
		• Lynn Peterson - Executive Chair
	Leadership & Governance	• Danny Brown - President and CEO
	• Board of Directors - 5 WLL representatives, including Mr. Peterson, and 5 OAS representatives,
			including Mr. Brown
	Significant Cost Savings	•	~$65MM/year in identified administrative and operational cost synergies by 2H23 anticipated
	and Operational Synergies	•	Will combine operational best practices to further advance efficiencies
		• New company name to be announced prior to closing
	Company & Headquarters	•	Combined company to be headquartered in Houston, TX
		• Denver office to remain in place for foreseeable future

	• Unanimously approved by WLL and OAS Boards of Directors
Approvals & Timing	•	Transaction subject to customary closing conditions, including the approval of WLL and OAS
	shareholders and regulatory approvals
	•	Expected closing in the second half of 2022

1)	Based on fully diluted shares outstanding	5