SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G/A

Under the Securities Exchange Act of 1934

(Amendment No. 3)

Forum Energy Technologies, Inc.

(Name of Issuer)

Common Stock, par value $0.01 per share

(Title of Class of Securities)

34984V 100

(CUSIP Number)

December 31, 2015

(Date of Event which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

¨ Rule 13d-1(b)

¨ Rule 13d-1(c)

x Rule 13d-1(d)

The information required in the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act, but shall be subject to all other provisions of the Act (however, see the Notes).

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920 Memorial City Way, Suite 1000

Houston, Texas 77024

Each of the following is hereinafter individually referred to as a “Reporting Person” and collectively as the “Reporting Persons.” This statement is filed on behalf of:

(i) L.E. Simmons, with respect to the shares of Common Stock indirectly owned by SCF-V, G.P., LLC, SCF-VI, G.P., Limited Partnership and SCF-VII, G.P., Limited Partnership and the shares of Common Stock directly owned by SCF 2012A, L.P. and SCF 2012B, L.P.;

(ii) L.E. Simmons & Associates, Incorporated, with respect to the shares of Common Stock indirectly owned by SCF-V, G.P., LLC, SCF-VI, G.P., Limited Partnership and SCF-VII, G.P., Limited Partnership and the shares of Common Stock directly owned by SCF 2012A, L.P. and SCF 2012B, L.P.;

(iii) SCF-V, L.P., with respect to shares directly owned by it;

(iv) SCF-V, G.P., LLC, with respect to shares directly owned by SCF-V, L.P.;

(v) SCF 2012A, L.P., with respect to shares directly owned by it;

(vi) SCF-VI, L.P., with respect to shares directly owned by it;

(vii) SCF-VI, G.P., Limited Partnership, with respect to shares directly owned by SCF-VI, L.P.;

(viii) SCF 2012B, L.P., with respect to shares directly owned by it;

(ix) SCF-VII, L.P., with respect to shares directly owned by it; and

(x) SCF-VII, G.P., Limited Partnership, with respect to shares directly owned by SCF-VII, L.P.

The address and principal business office of the Reporting Persons is:

600 Travis Street, Suite 6600

Houston, Texas 77002

L.E. Simmons is a United States citizen.

L.E. Simmons & Associates, Incorporated is a corporation organized under the laws of the State of Delaware.

SCF-V, L.P. is a limited partnership organized under the laws of the State of Delaware.

SCF-V, G.P., LLC is a limited liability company organized under the laws of the State of Delaware.

SCF 2012A, L.P. is a limited partnership organized under the laws of the State of Delaware.

SCF-VI, L.P. is a limited partnership organized under the laws of the State of Delaware.

SCF-VI, G.P., Limited Partnership is a limited partnership organized under the laws of the State of Delaware.

SCF 2012B, L.P. is a limited partnership organized under the laws of the State of Delaware.

SCF-VII, L.P. is a limited partnership organized under the laws of the State of Delaware.

SCF-VII, G.P., Limited Partnership is a limited partnership organized under the laws of the State of Delaware.

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(1) Includes 8,173,774 shares of Common Stock owned directly by SCF-V, L.P. SCF-V, G.P., LLC is the general partner of SCF-V, L.P. and has the power to direct the affairs of SCF-V, L.P., including decisions regarding the voting and disposition of the shares of Common Stock of Forum Energy Technologies, Inc. held by SCF-V, L.P.

(2) Includes 4,780,622 shares of Common Stock owned directly by SCF-VI, L.P. SCF-VI, G.P., Limited Partnership is the general partner of SCF-VI, L.P. and has the power to direct the affairs of SCF-VI, L.P., including decisions regarding the voting and disposition of the shares of Common Stock of Forum Energy Technologies, Inc. held by SCF-VI, L.P.

(3) Includes 7,694,241 shares of Common Stock owned directly by SCF-VII, L.P. SCF-VII, G.P., Limited Partnership is the general partner of SCF-VII, L.P. and has the power to direct the affairs of SCF-VII, L.P., including decisions regarding the voting and disposition of the shares of Common Stock of Forum Energy Technologies, Inc. held by SCF-VII, L.P.

(4) Includes 8,173,774 shares of Common Stock owned by SCF-V, L.P., 2,293,605 shares of Common Stock owned by SCF 2012A, L.P., 4,780,622 shares of Common Stock owned by SCF-VI, L.P., 1,315,558 shares of Common Stock owned by SCF 2012 B, L.P., and 7,694,241 shares of Common Stock owned by SCF-VII, L.P. L.E. Simmons & Associates, Incorporated, the general partner of SCF-V, G.P., LLC, SCF 2012A, L.P., SCF-VI, G.P., Limited Partnership, SCF2012B, L.P. and SCF-VII, G.P., Limited Partnership, has the power to direct the affairs of such entities, including decisions regarding the voting and disposition of the shares of Common Stock of Forum Energy Technologies, Inc. held by SCF-V, L.P. SCF 2012A, L.P., SCF-VI, L.P., SCF 2012 B, L.P. and SCF-VII, L.P.

(5) Includes 8,173,774 shares of Common Stock owned by SCF-V, L.P., 2,293,605 shares of Common Stock owned by SCF 2012A, L.P., 4,780,622 shares of Common Stock owned by SCF-VI, L.P., 1,315,558 shares of Common Stock owned by SCF 2012 B, L.P., and 7,694,241 shares of Common Stock owned by SCF-VII, L.P. L.E. Simmons is the President and sole stockholder of L.E. Simmons & Associates, Incorporated and in that capacity may be deemed to beneficially own all of the shares of Common Stock of Forum Energy Technologies, Inc. deemed to be beneficially owned by L.E. Simmons & Associates, Incorporated.

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SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: February 1, 2016