13D Filing: Blue Mountain Capital and Ocean Rig UDW Inc.

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE 13D

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. )*

OCEAN RIG UDW
INC.

(Name of Issuer)

Common Stock, par value $0.01 per share

(Title of Class of Securities)

G66964118

(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)

September 22, 2017

(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).

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Item 1. Security of the Issuer.

This Schedule 13D
relates to the shares of Common Stock, par value $0.01 per share (the Common Stock), of Ocean Rig UDW Inc., a Cayman Islands corporation (the Issuer). The Issuers principal executive office is located at
c/o Ocean Rig Cayman Management Services SEZC Limited, 3^rd Floor Flagship Building, Harbour Drive, Grand Cayman, Cayman Islands.

Item 2. Identity and Background.

(a-c) This
Statement is being filed by the following beneficial owners of Common Stock (each, a Reporting Person):

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The principal business of: (i) each of the BlueMountain Funds is to serve as a private investment fund; (ii) each of BMCA GP, BMF GP, BMGP GP, BMM
GP, BMST GP and BMKH GP is to serve as the general partner of BMCA, BMF, BMGP, BMM, BMST and BMKH, respectively; (iii) BMC GP is to serve as the sole owner of BMCA GP; (iv) GP Holdings is to serve as the sole owner of each of the General
Partners; and (v) the Investment Manager is to serve as the sole owner of BMM GP and to serve as investment manager to, and to make investment decisions on behalf of, the BlueMountain Funds.

The executive officers, directors and control persons of the Reporting Persons are as follows:

The business address of BMCA, BMCA GP, BMF, BMKH and BMT is c/o Maples Corporate Services Limited, P.O. Box 309, Ugland House,
Grand Cayman, KY1-1104, Cayman Islands. The business address of BMGP, BMST, each General Partner, GP Holdings, the Investment Manager, Mr. Feldstein, Mr. Liberman, Mr. Siderow, Mr. Smith, Mr. Dalton, Mr. Friedman,
Mr. Gerstein, Ms. Gile, Mr. Reeves and Mr. Shapiro is 280 Park Avenue, 12th Floor, New York, New York 10017. The business address of Mr. Groome and Mr. Linford is c/o HighWater, Pavilion Commercial Centre, 1st Floor,
802 West Bay Road, P.O. Box 30599, KY1-1203, Grand Cayman, Cayman Islands. The business address of each of BMM, BMM GP and Ms. Stevens is 6D, Route de Treves, L-2633 Seningerberg, Luxembourg B176.316.

(d) None of the Reporting Persons or any of their respective executive officers, directors or control persons has, during the last five years, been convicted
in a criminal proceeding (excluding traffic violations or similar misdemeanors).

(e) None of the Reporting Persons or any of their respective executive
officers, directors or control persons has, during the last five years, been a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and, as a result of such proceeding, was or is subject to a judgment, decree or
final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

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(f) Mr. Feldstein, Mr. Liberman, Mr. Siderow, Mr. Smith, Mr. Dalton, Mr. Friedman, Mr. Gerstein, Ms. Gile,
Mr. Groome, Mr. Reeves and Mr. Shapiro are U.S. citizens. Mr. Linford is a South African citizen. Ms. Stevens is a British citizen.

Item 3. Source and Amount of Funds or Other Consideration

BMCM and the BlueMountain Funds were issued 9,846,060 shares of Common Stock by the Issuer on the Restructuring Effective Date (as defined in Item 4). The
information set forth in Item 4 of this Schedule 13D is hereby incorporated herein by reference.

Item 4. Purpose of Transaction.

(1) During the second quarter of 2016, the board of directors of the Issuer (the Board) and a number of creditors formed the conclusion
that the Issuers debt obligations would need to be amended or exchanged for new debt and/or equity securities; (2) on August 11, 2016, the Issuer made a public announcement stating that it was exploring restructuring options; and
(3) on March 23, 2017, a Restructuring Agreement (the Restructuring Agreement) was executed between the Issuer and certain of its creditors to implement schemes of arrangement under the Companies Law of the Cayman
Islands (the Schemes) and to appoint joint provisional liquidators, as part of the proposed restructuring.

The Schemes were sanctioned
and confirmed by the Grand Court of the Cayman Islands on September 15, 2017 (Cayman Islands time). All of the conditions of the Schemes having been fulfilled, the Schemes became effective on September 22, 2017 (Cayman Islands time) (the
Restructuring Effective Date).

Pursuant to the Schemes, and subject to the conditions described therein, BMCM and the BlueMountain
Funds acquired beneficial ownership of 9,846,060 shares of Common Stock. Following consummation of the Schemes, the Issuer intends to conduct an extraordinary general meeting to adopt an amended and restated memorandum and articles of association
to, among other things, increase the number of directors serving on its Board to seven. Pursuant to these amended articles of association: (i) if there are three or fewer holders, together with each of their affiliates, each with at least 7.5%
of the outstanding shares of Common Stock, then each will be entitled to appoint a director to the Board; and (ii) if there are more than three holders, together with each of their affiliates, each with at least 7.5% of the outstanding shares
of Common Stock, then three persons entitled to appoint a director to the Board shall be designated by the majority vote of the shares of all the 7.5% holders. If any holder, together with its affiliates, holds 17% or more of the outstanding shares
of Common Stock, such holder shall automatically be one of such three persons entitled to appoint a director to the Board.

The summary of the
Restructuring Agreement and the Schemes set forth above does not purport to be complete and is qualified in its entirety by reference to the text of the Restructuring Agreement, the press release of the Issuer dated July 21, 2017 and the press
release of the Issuer dated September 22, 2017, copies of which are being filed as Exhibits 2, 3 and 4, respectively, and are incorporated herein by reference.

The Reporting Persons acquired the Common Stock for investment purposes. The Reporting Persons acquired the Common Stock over which they exercise beneficial
ownership in the belief that the Common Stock represents an attractive investment opportunity. The Reporting Persons intend to review their investment in the Issuer on a continuing basis. Representatives of the Reporting Persons may have
discussions from time to time with the Issuer, other stockholders and third parties relating to the Issuer, strategic alternatives that may be available to the Issuer and the Issuers business, operations, assets, capitalization, financial
condition, governance, management and future plans, including in respect of one or more of the actions described in subsections (a) through (j) of Item 4 of Schedule 13D. There can be no assurance as to the outcome of any of the
discussions referred to in this Schedule 13D.

Depending on various factors, including the Issuers financial position and strategic direction, the
outcome of the discussions referenced above, actions taken by the Board, price levels of the securities of the Issuer, other investment opportunities available to the Reporting Persons, the availability and cost of debt financing, the availability
of potential business combination and other strategic transactions, conditions in the capital markets and general economic and industry conditions, the Reporting Persons may in the future take such actions with respect to their investments in the
Issuer as they deem appropriate, including acquiring or disposing of securities of the Issuer, entering into financial instruments or other agreements which increase or decrease the Reporting Persons economic exposure with respect to their
investments in the Issuer, engaging in any hedging or similar transactions with respect to such holdings and/or otherwise changing their intention with respect to any and all matters referred to in Item 4 of Schedule 13D.

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Item 5. Interest in Securities of the Issuer.

(a-b)
All percentages set forth in this Schedule 13D are based on the Issuers 90,660,769 shares of Common Stock outstanding as of September 22, 2017, as confirmed to the Reporting Persons by the Issuer on September 22, 2017. The
information set forth in Rows 7-13 of each Cover Page of this Schedule 13D is hereby incorporated herein by reference.

The General Partners, BMCA
GP, BMM GP and GP Holdings expressly declare that this filing shall not be construed as an admission that each is, for the purposes of sections 13(d) or 13(g) of the Act, the beneficial owner of any securities covered by this filing.

None of the Reporting Persons beneficially own any other shares of Common Stock of the Issuer.

(c) During the last 60 days, no transactions in the Common Stock were effected by any of the Reporting Persons.

(d) No person other than a Reporting Person has the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of
shares of, Common Stock beneficially owned by the Reporting Persons.

(e) Not applicable.

Item 6. Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer.

The information set forth in Item 4 of this Schedule 13D is hereby incorporated herein by reference.

Except for the BlueMountain Funds, none of the Reporting Persons is a party to any contract, arrangement, understanding or relationship with respect to any
securities of the Issuer.

On the Restructuring Effective Date, pursuant to the Schemes, the Issuer and certain of its subsidiaries, as borrowers and
guarantors, entered into a new credit agreement dated September 22, 2017 (the Credit Agreement) with the BlueMountain Funds and certain other creditors of the Issuer (the Lenders), which Credit Agreement
contains limited financial covenants. In addition, the Issuer and certain of its subsidiaries will guarantee the obligations of the Credit Agreement and collateral has been granted to the Lenders by way of a first priority lien over substantially
all existing and newly acquired assets of the borrowers and guarantors. The Credit Agreement consists of an about $450 million senior secured term loan facility bearing interest at 8.00% per annum with a maturity date of September 20,
2024.

Also on the Restructuring Effective Date, the Issuer entered into a Governance Agreement dated September 22, 2017 (the Governance
Agreement) with the BlueMountain Funds and certain other creditors of the Issuer receiving Common Stock pursuant to the Schemes. The Governance Agreement provides for certain governance and shareholders rights, including customary
registration rights.

The summary of the Credit Agreement and the Governance Agreement set forth above does not purport to be complete and is qualified in
its entirety by reference to the text of the Credit Agreement and the Governance Agreement, copies of which are being filed as Exhibits 5 and 6, respectively, and are incorporated herein by reference.

Item 7. Material to be Filed as Exhibits.

1. Joint
Filing Agreement dated September 29, 2017, attached as Exhibit 1 hereto.

2. Restructuring Agreement (incorporated herein by reference to Exhibit 10.1
to Form 6-K filed by the Issuer on March 28, 2017).

3. Press Release of the Issuer dated as of July 21, 2017 (incorporated herein by reference
to Exhibit 99.1 to Form 6-K filed by the Issuer on July 21, 2017).

4. Press Release dated as of September 22, 2017 (incorporated herein by
reference to Exhibit 99.1 to Form 6-K filed by the Issuer on September 22, 2017).

5. Credit Agreement (incorporated herein by reference to Exhibit
10.1 to Form 6-K filed by the Issuer on September 22, 2017).

6. Governance Agreement (incorporated herein by reference to Exhibit 10.3 to Form 6-K
filed by the Issuer on September 22, 2017).

SIGNATURES

After reasonable inquiry and to the best knowledge and belief of the undersigned, the undersigned certifies that the information set forth in this statement
with respect to the undersigned is true, complete and correct.

Date: September 29, 2017

The original statement shall be signed by each person on whose behalf the statement is filed or his authorized
representative. If the statement is signed on behalf of a person by his authorized representative (other than an executive officer or general partner of the filing person), evidence of the representatives authority to sign on behalf of such
person shall be filed with the statement; provided, however, that a power of attorney for this purpose which is already on file with the Commission may be incorporated by reference. The name and any title of each person who signs the
statement shall be typed or printed beneath his signature.

ATTENTION: INTENTIONAL MISSTATEMENTS OR OMISSIONS OF FACT CONSTITUTE FEDERAL CRIMINAL
VIOLATIONS (SEE 18 U.S.C. 1001)