Exhibit 4.1

MAXIMUM CREDIT AMOUNT INCREASE AGREEMENT

THIS MAXIMUM CREDIT AMOUNT INCREASE AGREEMENT (this “Agreement”) dated as of December 19, 2014 is between JPMorgan Chase Bank, N.A., Wells Fargo Bank, N.A., Bank of America, N.A., Compass Bank, U.S. Bank National Association, Capital One, National Association and SunTrust Bank (each an “Existing Lender” and collectively, “Existing Lenders”), Whiting Oil and Gas Corporation, a Delaware corporation (“Borrower”), Whiting Petroleum Corporation, a Delaware corporation (the “Parent Guarantor”), and JPMorgan Chase Bank, N.A., as administrative agent (in such capacity, together with its successors in such capacity, the “Administrative Agent”) for the lenders party to the Credit Agreement referred to below. Each capitalized definitional term used herein but not otherwise defined herein has the meaning given such term in the Credit Agreement.

R E C I T A L S

A. The Borrower, the Parent Guarantor, the Administrative Agent and certain Lenders and agents have heretofore entered into that certain Sixth Amended and Restated Credit Agreement, dated as of August 27, 2014 as amended from time to time (the “Credit Agreement”).

B. The Borrower has heretofore requested pursuant to Section 2.06 of the Credit Agreement that the Aggregate Maximum Revolving Credit Amounts be increased to $3,500,000,000 by increasing the Maximum Revolving Credit Amount of the Existing Lenders.

C. NOW, THEREFORE, in consideration of the premises and the mutual covenants herein contained, for good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties hereto agree as follows:

Section 1.01 Commitment Increase.

(a) Pursuant to Section 2.06(c) of the Credit Agreement, effective as of the Effective Date (used herein as defined below) the Existing Lenders’ respective Maximum Revolving Credit Amounts are hereby increased as set forth on Annex 1 attached hereto.

(b) Effective as of the Effective Date the increase in each Existing Lender’s Maximum Revolving Credit Amount hereby supplements Annex I to the Credit Agreement, such that after giving effect to the inclusion of each Maximum Revolving Credit Amount increase contemplated hereby, Annex I to the Credit Agreement is amended and restated to read as set forth on Schedule 2.06 attached hereto.

Section 1.02 Waiver of Processing and Recordation Fee. The Administrative Agent hereby waives the processing and recordation fee of $3,500 required to be delivered in connection with this Agreement pursuant to Section 2.06 of the Credit Agreement.

Section 1.03 Representations and Warranties; Agreements. Each Existing Lender hereby: (a) represents and warrants that (i) it has full power and authority, and has taken all action necessary, to execute and deliver this Agreement and to consummate the transactions

contemplated hereby, (ii) it has received a copy of the Credit Agreement, together with copies of the most recent financial statements delivered thereunder, and such other documents and information as it has deemed appropriate to make its own credit analysis and decision to enter into this Agreement and to increase its Revolving Commitment, on the basis of which it has made such analysis and decision independently and without reliance on the Administrative Agent or any other Lender; and (b) agrees that (i) it will, independently and without reliance on the Administrative Agent or any other Lender, and based on such documents and information as it shall deem appropriate at the time, continue to make its own credit decisions in taking or not taking action under the Credit Agreement, and (ii) it will perform in accordance with the terms of the Credit Agreement, all of the obligations which by the terms of the Credit Agreement are required to be performed by it as a Lender (including, without limitation, any obligations of it, if any, under Section 2.06(c) of the Credit Agreement).

Section 1.04 Effectiveness. This Agreement shall become effective as of December 19, 2014 (the “Effective Date”), subject to the Administrative Agent’s receipt of counterparts of this Agreement duly executed on behalf of the Existing Lenders and the Borrower.

Section 1.05 Counterparts. This Agreement may be executed in counterparts (and by different parties hereto on different counterparts), each of which shall constitute an original, but all of which when taken together shall constitute a single contract. Delivery of an executed counterpart of a signature page of this Agreement by facsimile or other electronic image scan transmission shall be as effective as delivery of a manually executed counterpart of this Agreement.

Section 1.06 Governing Law. THIS AGREEMENT SHALL BE CONSTRUED IN ACCORDANCE WITH AND GOVERNED BY THE LAWS OF THE STATE OF NEW YORK.

Section 1.07 Severability. In case any one or more of the provisions contained in this Agreement should be held invalid, illegal or unenforceable in any respect, none of the parties hereto shall be required to comply with such provision for so long as such provision is held to be invalid, illegal or unenforceable, but the validity, legality and enforceability of the remaining provisions contained herein and in the Credit Agreement shall not in any way be affected or impaired. The parties hereto shall endeavor in good-faith negotiations to replace the invalid, illegal or unenforceable provisions with valid provisions the economic effect of which comes as close as possible to that of the invalid, illegal or unenforceable provisions.

Section 1.08 Notices. All communications and notices hereunder shall be in writing and given as provided in Section 12.01 of the Credit Agreement.

[Signature Page to Follow]

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IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be duly executed as of the date first written above.

[Signature Page to Maximum Credit Amount Increase Agreement]

[Signature Page to Maximum Credit Amount Increase Agreement]

[Signature Page to Maximum Credit Amount Increase Agreement]

[Signature Page to Maximum Credit Amount Increase Agreement]

[Signature Page to Maximum Credit Amount Increase Agreement]

[Signature Page to Maximum Credit Amount Increase Agreement]

[Signature Page to Maximum Credit Amount Increase Agreement]

[Signature Page to Maximum Credit Amount Increase Agreement]

Annex 1

SCHEDULE 2.06

LIST OF MAXIMUM REVOLVING CREDIT AMOUNTS AFTER

MAXIMUM CREDIT AMOUNT INCREASE AGREEMENT

Aggregate Maximum Credit Amounts