Exhibit 5.1

Fulbright Tower • 1301 McKinney, Suite 5100 • Houston, Texas 77010-3095

Telephone: 713 651 5151 • Facsimile: 713 651 5246

January 18, 2013

Offshore Group Investment Limited

c/o Vantage Drilling Company

777 Post Oak Boulevard, Suite 800

Houston, Texas 77056

Ladies and Gentlemen:

We have acted as special counsel for Offshore Group Investment Limited, a Cayman Islands exempted company (the “Company”), Vantage Drilling Company, a Cayman Islands exempted company (the “Parent”), and their subsidiaries listed on Schedule I hereto (the “Subsidiary Guarantors”) with respect to the preparation of the Registration Statement on Form S-4 (the “Registration Statement”) filed with the Securities and Exchange Commission (the “Commission”) in connection with the registration by the Company under the Securities Act of 1933, as amended (the “Securities Act”), of the offer to exchange (the “Exchange Offer”) (i) up to $1,150,000,000 aggregate principal amount of the Company’s 7.5% Senior Secured First Lien Notes due 2019 (the “Exchange Notes”) for a like principal amount of the Company’s outstanding 7.5% Senior Secured First Lien Notes due 2019 (the “Outstanding Notes”) and (ii) the guarantees (the “Guarantees”) of the Parent and the Subsidiary Guarantors of the Outstanding Notes and the Exchange Notes. The Outstanding Notes were issued, and the Exchange Notes will be issued, under an Indenture dated as of October 25, 2012 (the “Indenture”), among the Company, the Subsidiary Guarantors and Wells Fargo Bank, National Association, as trustee (the “Trustee”). Capitalized terms used but not defined herein shall have the meaning given such terms in the Indenture.

We have examined originals or copies, certified or otherwise identified to our satisfaction, of (i) the Registration Statement, (ii) the Indenture, (iii) the Registration Rights Agreement, (iv) the certificate of incorporation and bylaws of Vantage Deepwater Drilling, Inc., a Delaware corporation and a Subsidiary Guarantor, (v) the certificate of formation and limited liability company agreement of Vantage Delaware Holdings, LLC, a Delaware limited liability company and a Subsidiary Guarantor, and (vi) such other certificates, statutes and other instruments and documents as we considered appropriate for purposes of the opinions hereafter expressed.

In connection with this opinion, we have assumed that (i) the Indenture has been duly authorized, executed and delivered by, and represents the valid and binding obligation of, the Trustee, (ii) the Registration Statement, and any amendments thereto (including post-effective amendments), will have become effective under the Securities Act and (iii) the Exchange Notes will be issued in compliance with applicable federal and state securities laws and in the manner described in the Registration Statement.

AUSTIN • BEIJING • DALLAS • DENVER • DUBAI • HONG KONG • HOUSTON • LONDON • LOS ANGELES • MINNEAPOLIS

MUNICH • NEW YORK • PITTSBURGH-SOUTHPOINTE • RIYADH • SAN ANTONIO • ST. LOUIS • WASHINGTON DC

www.fulbright.com

Offshore Group Investment Limited

January 18, 2013

Page 2

Based upon and subject to the foregoing and the limitations, qualifications, exceptions and assumptions set forth herein, and having regard for such legal considerations as we deem relevant, we are of the opinion that, when the Exchange Notes (in the form examined by us) have been duly executed by the Company, the Parent and the Subsidiary Guarantors, authenticated by the Trustee in accordance with the terms of the Indenture and delivered upon consummation of the Exchange Offer against receipt of Outstanding Notes surrendered in exchange therefor in accordance with the terms of the Exchange Offer, the Indenture and the Registration Rights Agreement, the Exchange Notes will be valid and binding obligations of the Company and the Guarantees will be valid and binding obligations of the Parent and the Subsidiary Guarantors.

The enforceability of the Exchange Notes may be limited or affected by (a) bankruptcy, insolvency, reorganization, moratorium, liquidation, rearrangement, probate, conservatorship, fraudulent transfer, fraudulent conveyance and other similar laws (including court decisions) now or hereafter in effect and affecting the rights and remedies of creditors generally or providing for the relief of debtors, (b) the refusal of a particular court to grant (i) equitable remedies, including, without limiting the generality of the foregoing, specific performance and injunctive relief, or (ii) a particular remedy sought under such documents as opposed to another remedy provided for therein or another remedy available at law or in equity, (c) general principles of equity (regardless of whether such remedies are sought in a proceeding in equity or at law) and (d) judicial discretion.

The opinions expressed herein are limited exclusively to the laws of the State of New York, the General Corporation Law of the State of Delaware and the Delaware Limited Liability Company Act, and we are expressing no opinion as to the effect of the laws of any other jurisdiction, domestic or foreign. With respect to the opinions set forth above, to the extent such opinions relate to the laws of the Cayman Islands, Hungary, Malaysia, the Netherlands, Cyprus, Poland or Indonesia, we have relied solely on the opinions of Maples and Calder, Reti, Antall & Partners Law Firm, Azmi & Associates, Huessen Law Firm, Ioannides Demetriou LLC, PricewaterhouseCoopers Legal Szurminska-Jaworska Sp.K. and Hadromi & Partners Law Firm, respectively, a copy of each of which is being filed as an exhibit to the Registration Statement and such opinions are based upon and subject to the assumptions, qualifications, limitations and exclusions set forth in such opinions, which are incorporated herein by reference.

Offshore Group Investment Limited

January 18, 2013

Page 3

We hereby consent to the filing of this opinion as an exhibit to the Registration Statement and to the use of our firm name in the prospectus forming a part of the Registration Statement under the caption “Legal Matters.” In giving this consent, we do not thereby admit that we are included in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission. This opinion is expressed as of the date hereof, and we disclaim any undertaking to advise you of any subsequent changes in the facts stated or assumed herein or of any subsequent changes in applicable law.

Very truly yours,

/s/ Fulbright & Jaworski L.L.P.

Fulbright & Jaworski L.L.P.

Schedule I

Name	Jurisdiction of Incorporation or Organization
Vantage Holding Hungary Kft		Hungary
Vantage Drilling Netherlands B.V.		The Netherlands
P2020 Rig Co.		Cayman Islands
P2021 Rig Co.		Cayman Islands
Emerald Driller Company		Cayman Islands
Sapphire Driller Company		Cayman Islands
Vantage Driller I Co.		Cayman Islands
Vantage Driller II Co.		Cayman Islands
Vantage Driller III Co.		Cayman Islands
Vantage Driller IV Co.		Cayman Islands
Vantage Drilling Labuan I Ltd.		Malaysia/Labuan
Vantage Drilling (Malaysia) I Sdn. Bhd.		Malaysia
Vantage Holdings Malaysia I Co.		Cayman Islands
Vantage International Management Co.		Cayman Islands
Dragonquest Holdings Company		Cayman Islands
Vantage Holdings Cyprus ODC Limited		Cyprus
Vantage Drilling Poland—Luxembourg Branch		Poland
Vantage Deepwater Company		Cayman Islands
Vantage Deepwater Drilling, Inc.		Delaware
Vantage Delaware Holdings, LLC		Delaware
Tungsten Explorer Company		Cayman Islands
PT. Vantage Drilling Company Indonesia		Indonesia