BlueMountain Capital Trims Stake in Overseas Shipholding Group Inc (OSG)

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE 13D

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 1)*

OVERSEAS
SHIPHOLDING GROUP, INC.

(Name of Issuer)

Class A Common Stock, par value $0.01 per share

(Title of Class of Securities)

69036R 103

(CUSIP
Number)

Eric M. Albert

BlueMountain Capital Management, LLC

280 Park Avenue, 12^th Floor

New York, New York 10017

212-905-5647

(Name,
Address and Telephone Number of Person Authorized to Receive Notices and Communications)

March 11, 2016

(Date of Event which Requires Filing of this Statement)

If the filing person has
previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.  ¨

Note:Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See §
240.13d-7 for other parties to whom copies are to be sent.

The information required on 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).