Table of Contents

As filed with the Securities and Exchange Commission on April 18, 2007

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 20-F

(Mark One)

OR

For the fiscal year ended November 30, 2006

OR

For the transition period from                     to

OR

Date of event requiring this shell company report

Commission File Number 00-21742

ACERGY S.A.

(Exact name of Registrant as specified in its charter)

LUXEMBOURG

(Jurisdiction of incorporation or organization)

c/o Acergy M.S. Limited

Dolphin House, Windmill Road, Sunbury-on-Thames

Middlesex TW16 7HT England

(Address of principal executive offices)

Securities registered or to be registered pursuant to Section 12(b) of the Act:

Securities registered or to be registered pursuant to Section 12(g) of the Act:

None

Securities for which there is a reporting obligation pursuant to Section 15(d) of the Act:

None

Indicate the number of outstanding shares of each of the issuer’s classes of capital or common stock as of the close of the period covered by the annual report:

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Exchange Act.     x   Yes     ¨   No

If this report is an annual or transition report, indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or 15(d) of the Securities Act of 1934.     ¨   Yes     x   No

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.     x   Yes     ¨   No

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, or a non- accelerated filer. See definition of “accelerated filer and large accelerated filer” in Rule 12b-2 of the Exchange Act. (Check one):

Indicate by check mark which financial statement item the registrant has elected to follow.

¨     Item 17             x     Item 18

If this is an annual report, indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act)     ¨   Yes     x   No

Table of Contents

TABLE OF CONTENTS

i

Table of Contents

ii

Table of Contents

INTRODUCTION

Acergy S.A. is a Luxembourg registered company. In this Report, the terms “we,” “us,” “our” and “Acergy” refer to Acergy S.A. and, unless the context otherwise requires, its consolidated subsidiaries. References to Acergy activities by years refer to fiscal years ended November 30. Our Common Shares are traded on the Nasdaq Global Select Market in the form of American Depositary Shares (“ADSs”) (each ADS representing one Common Share) under the ticker symbol “ACGY” and are listed on Oslo Børs under the ticker symbol “ACY.”

As of March 31, 2007, we had outstanding 194,953,972 Common Shares.

BASIS OF PRESENTATION

The consolidated financial statements, including the notes thereto, included in this Report (the “Consolidated Financial Statements”) have been prepared in accordance with accounting principles generally accepted in the United States (“U.S. GAAP”). Our consolidated financial statements are subject to the approval of our shareholders each year at the annual general meeting of shareholders.

Unless otherwise specified or unless the context otherwise requires, references in this Report to “$” are to the U.S. dollar, references to “NOK” are to the Norwegian kroner, references to “GBP” are to the British pound sterling and references to “EUR” are to the Euro, the lawful currency of the participating member states of the European Union.

SPECIAL NOTE REGARDING FORWARD LOOKING STATEMENTS

Certain statements made in this Report and some of the documents incorporated by reference in this Report may include “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933, as amended (the “Securities Act”), and Section 21E of the U.S. Securities Exchange Act of 1934, as amended (the “Exchange Act”). These statements relate to our expectations, beliefs, intentions or strategies regarding the future. These statements may be identified by the use of words like “anticipate,” “believe,” “estimate,” “expect,” “intend,” “may,” “plan,” “project,” “will,” “should,” “seek,” and similar expressions. In this Report, they include statements contained under Item 3. “Key Information—Risk Factors,” Item 4. “Information on the Company,” Item 5. “Operating and Financial Review and Prospects,” Item 6. “Directors, Senior Management and Employees,” Item 7. “Major Shareholders and Related Party Transactions,” Item 8. “Financial Information,” Item 9. “The Offer and Listing,” Item 10. “Additional Information,” Item 11. “Quantitative and Qualitative Disclosures about Market Risk,” and Item 15. “Controls and Procedures.”

The forward-looking statements that we make reflect our current views and assumptions with respect to future events and are subject to risks and uncertainties. Actual and future results and trends could differ materially from those set forth in such statements due to various factors, including those discussed in this Report under Item 3. “Key Information—Risk Factors,” Item 5. “Operating and Financial Review and Prospects” and Item 11. “Quantitative and Qualitative Disclosures about Market Risk.”

The following factors, and others which are discussed in our public filings with the U.S. Securities and Exchange Commission (the “SEC”) including this Report, are among those that may cause actual and future results and trends to differ materially from our forward-looking statements: (i) our ability to deliver fixed price projects in accordance with client expectations and the parameters of our bids and avoid cost overruns; (ii) our ability to collect receivables, negotiate variation orders and collect the related revenues; (iii) our ability to recover costs on significant projects; (iv) capital expenditures by oil and gas companies; (v) oil and gas prices; (vi) delays or cancellation of projects included in our backlog; (vii) general economic conditions and competition

1

Table of Contents

in the markets and businesses in which we operate; (viii) prevailing prices for our products and services; (ix) the loss of, or deterioration of our relationship with, any significant clients; (x) the outcome of legal proceedings or governmental inquiries; (xi) uncertainties inherent in operating internationally, including economic, political and social instability, boycotts or embargoes, labor unrest, changes in foreign governmental regulations, corruption and currency fluctuations; (xii) liability to third parties for the failure of our joint venture partners to fulfill their obligations; (xiii) changes in, or our failure to comply with, applicable laws and regulations; (xiv) cost and availability of raw materials; (xv) operating hazards, including spills, environmental damage, personal or property damage and business interruptions caused by adverse weather; (xvi) equipment or mechanical failures which could increase costs, impair revenues and result in penalties for failure to meet project completion requirements; (xvii) the timely delivery of ships on order and the timely completion of ship conversion programs; (xviii) the impact of accounting for projects on a “percentage-of-completion” basis, which could reduce or eliminate reported profits; (xix) adverse weather conditions; (xx) our ability to keep pace with technological changes; (xxi) the effectiveness of our disclosure controls and procedures and internal controls over financial reporting; and (xxii) other factors which are described from time to time in our public filings with the SEC.

Many of these factors are beyond our ability to control or predict. Given these uncertainties, you should not place undue reliance on the forward-looking statements. We undertake no obligation to update publicly or revise any forward-looking statements, whether as a result of new information, future events or otherwise.

Neither our independent registered public accountants, nor any other independent accountants, have compiled, examined, or performed any procedures with respect to the forward-looking financial information contained herein, nor have they expressed any opinion or any other form of assurance on such information or its achievability, and assume no responsibility for, and disclaim any association with, the prospective financial information.

PART I