6-K

QuickLinks -- Click here to rapidly navigate through this document

FORM 6-K

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

REPORT OF FOREIGN ISSUER

Pursuant to Rule 15d-16 of
the Securities Exchange Act of 1934

For the month of October, 2002

STOLT OFFSHORE S.A.
(Translation of registrant's name into English)

c/o Stolt Offshore M.S. Ltd.
Dolphin House
Windmill Road
Sunbury-on-Thames
Middlesex TW16 7HT
ENGLAND
(Address of principal executive offices)

        In accordance with General Instruction B, item (iii), attached herewith is Press Release dated October 7, 2002 announcing financial results for the registrant's Third Quarter (ended August 31, 2002) of Fiscal Year 2002 and additional management changes.

        This report shall be deemed to be incorporated by reference into the registrant's Registration Statement on Form F-3 (File No. 333-86288) and Registration Statements on Form S-8 (File Nos. 333-74321, 333-09292 and 333-85168) and to be a part of such registration statements from the date on which this report is filed, to the extent not superseded by documents or reports subsequently filed.

        Certain statements contained in the press release filed pursuant to this Form 6-K are "forward-looking" statements within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. These statements relate to the registrant's 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," and "seek" and similar expressions.

        The forward-looking statements that the registrant makes reflect its 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 risk factors listed from time to time in the registrant's filings with the Securities and Exchange Commission. Many of these factors are beyond the registrant's ability to control or predict. Given these uncertainties, you should not place undue reliance on the forward-looking statements. The registrant undertakes no obligation to update publicly or revise any forward-looking statements, whether as a result of new information, future events or otherwise.

SIGNATURES

        Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

Date: October 15, 2002

STOLT OFFSHORE S.A.
By:	/s/  ALAN B. WINSOR Alan B. Winsor, Attorney-in-Fact

QuickLinks

SIGNATURES

EX-99.1

QuickLinks -- Click here to rapidly navigate through this document

A subsidiary of Stolt-Nielsen S.A.	C/o Stolt Offshore M.S. Limited Dolphin House Windmill Road Sunbury-on-Thames Middlesex, TW16 7HT England	Tel: + 44 1932 773700 Fax: + 44 1932 773701 www.stoltoffshore.com
	Contact:	Richard M. Lemanski     US +1 (203) 625 3604     UK +44 1224 718436     rlemanski@stolt.com

Stolt Offshore S.A. Announces Third Quarter Results
And Additional Management Changes

London, England—October 7, 2002—Stolt Offshore S.A. (Nasdaq: SOSA; Oslo Stock Exchange: STO) today reported results for the third quarter and nine months ended August 31, 2002. The net loss for the quarter was $17.2 million, or $0.21 per share, on net operating revenue of $368.9 million, compared with a net income of $17.5 million, or $0.20 per share, on net operating revenue of $365.6 million for the same period last year. Excluding a one-off gain of $8.0 million on the sale of Big Inch Marine Systems, the net loss for the quarter was $25.2 million or $0.30 per share. The weighted-average number of common share equivalents outstanding for the quarter was 83.1 million compared with 87.2 million for the same period of 2001.

        For the nine-month period ended August 31, 2002 the Company reported a net loss of $12.1 million, or $0.14 per share, on net operating revenue of $996.4 million. This compares with a net loss of $4.3 million, or $0.05 per share, on net operating revenue of $838.7 million for the same period last year. Excluding a one-off gain of $8.0 million on the disposal of Big Inch Marine Systems, the net loss for the nine-month period ended August 31, 2002 was $20.1 million or $0.24 per share. The weighted-average number of common share equivalents outstanding for the latest nine-month period was 85.1 million compared with 87.2 million for the first nine months of last year.

        The Company today also announced, effective immediately, that Alan Brunnen, Chief Operating Officer and Joel Leroux, Director of Product Lines, are leaving the company. Bruno Chabas has been appointed the new Chief Operating Officer and Jan Chr. Engelhardtsen has been appointed interim Chief Financial Officer.

        Commenting on the quarterly result, Niels G. Stolt-Nielsen, interim Chief Executive Officer, said, "The result for the quarter is extremely disappointing. We have been too optimistic when calculating cost and time and have failed to make reserves for delays and faults of subcontractors nominated by our clients. This has resulted in cost over-runs and operational problems on projects and a delay on a major pipelay contract in Nigeria. In addition we have a continued weak market in the Gulf of Mexico.

        "Our industry is suffering as a consequence of customers requiring contractors to assume increased risks when we take on larger and more complex projects. We will, of course, continue to take on EPIC contracts as the market demands—it is the strategy of this company to be an EPIC contractor—but we will not accept contractually onerous terms, which we have in the past. Our preference is to contract high risk projects on a cost-plus basis or working as part of a consortium in order to spread risk and project profitability.

        "In Southern Europe, Africa and the Middle East, we have made progress on the Shell Bonga project in the design and procurement of the steel catenary risers which will be installed in a water depth of 1,000 meters in Nigeria in 2004. After completing the detailed engineering study for the installation and tie-in of the risers, we are now forecasting higher than expected fabrication and

installation costs mainly due to unforeseen anchorages of the flowlines and failure to perform by one of the main local contractors.

        "We continued on the installation work on the Burullus Scarab and Saffron project in Egypt, the first deepwater development in the Eastern Mediterranean. This has involved the installation of two 65-kilometer 24-inch and 36-inch diameter gas export trunk lines together with 40 kilometers of in-field flowlines, umbilicals and associated subsea structures. Cost over-runs on this project have been experienced due to changes in project planning, materials supplied by the customer that were both late and defective, and difficulties with a nominated sub-contractor requiring additional engineering, management and supervision costs.

        "The installation work for the Offshore Gas Gathering System (OGGS) project for Shell in Nigeria, the largest pipeline offshore West Africa, has now commenced. Progress on the pipelay work has however been delayed by late delivery of key items by a third party that is outside our control. This has had a negative impact on the utilization of the LB 200 pipelay barge. Earnings for this project previously expected in 2002 will be delayed until the first half of 2003. We also made progress on the fabrication of the deck that will shortly be installed by the Seaway Polaris on the OGGS Riser Platform.

        "Engineering work continues on both the Shell Forcados Yokri project in Nigeria and the ChevronTexaco Sanha Condensate project in Angola. Phase Two of the installation work on the TotalFinaElf Girassol and the Jasmine tie-in projects commence later in the year.

        "In the U.K. Region, we had a disappointing quarter due to pipeline burial problems on the Conoco CMS project and a general low level of activity. Pipeline burial is a high-risk activity, which has typically been contracted on a lump sum basis. We have now adopted a policy under which we will not take on this type of work on a lump sum basis, without sharing some of the risk with the client.

        "New contract awards in this region include a $41 million contract from NAM for the Neptunus K7 and K15 tie-back projects.

        "In the Norway Region we saw a high level of activity, good project delivery and improving margins on new project awards. We were awarded a $50 million contract from TotalFinaElf Norway for the tie-back of the Skirne and Byggve subsea wells to the Heimdal platform.

        "In the North America Region there has been a low level of activity and continuing weak margins throughout the quarter in the Gulf of Mexico. We recently received letters of intent for three projects for the DLB 801 pipelay barge. The largest project calls for the installation of 47 kilometres of 30-inch diameter gas pipeline across Boston Harbour as part of the Duke Energy Hubline project. The majority of activity for these projects is expected to occur during the latter part of the fourth quarter 2002 and the first quarter of 2003.

        "In Brazil, the Seaway Condor completed her upgrading in dry dock and is now capable of laying flexible flowlines in a water depth of 2,000 meters on her new four-year contract for Petrobras.

        "In Asia Pacific the Arwana pipelay barge had a 90-day pipelay program for TotalFinaElf on the Tunu project.

        "The Paragon engineering companies have seen a steady activity level, and satisfactory profits.

        "Our backlog now stands at $1.8 billion of which $488 million is for the remainder of 2002. This compares with a backlog of $1.6 billion for this time last year of which $378 million was for 2001. Contract awards during the third quarter totalled $210 million. The level of bids outstanding now stands at $3.7 billion, similar to this time last year.

        "In August 2002 the Company sold substantially all of the assets and business of Big Inch Marine Systems, Inc., which manufactures subsea pipeline connectors and flanges, for approximately $18 million to Oil States Industries, Inc.

2

        "In light of the disappointing results for Stolt Offshore, in late September the Company's Board of Directors agreed to accept an offer from Stolt-Nielsen S.A., the Company's parent, to exchange $40 million of debt owed by the Company to Stolt-Nielsen S.A. for 9.4 million Common shares at an exchange price of $4.25 per share. On completion of this transaction the total number of Common share equivalents outstanding is 93.3 million.

        "It is clear that we have excellent technologies, assets and a unique deepwater installation track record. However, despite the considerable effort and progress made during the past two years in improving project and risk management, we have failed in the execution of our EPIC projects. The new team will not change strategy, but will remove all internal obstacles that stand in the way for successful project tendering and execution.

        "Despite expected growth in the accessible market for our business from $10 billion this year to $15 billion in 2004, our entire industry is currently suffering with low profit levels due to customers loading more and more risks on their EPIC contractors without the necessary improved rewards. This situation must change for the offshore construction sector to become a healthy and viable industry," Mr. Stolt-Nielsen concluded.

        Stolt Offshore is a leading offshore contractor to the oil and gas industry, specialising in technologically sophisticated offshore and subsea engineering, flowline and pipeline lay, construction, inspection and maintenance services. The Company operates in Europe, the Middle East, West Africa, Asia Pacific, and the Americas.

        This news release contains forward-looking statements as defined in the U.S. Private Securities Litigation Reform Act of 1995. Actual future results and trends could differ materially from those set forth in such statements due to various factors. Additional information concerning these factors is contained from time to time in the Company's U.S. SEC filings, including but not limited to the Company's report on Form 20F/A for the year ended November 30, 2001. Copies of these filings may be obtained by contacting the Company or the SEC.

Conference Call Information		Replay Facility details
Lines will open 10 minutes prior to conference call		This facility is available from 12 noon EST (5pm BST) Monday October 7th, until 5pm EST (10pm BST), Monday October 14th.
Date:	Monday October 7th, 2002
Time:	10am EST (3pm BST)	Dialing from the UK:	0800 953 1533
Freephone Dial In Numbers:
UK	0800 953 0810	Dialing from the US:	1866 276 1167
USA	1 866 789 2220
Norway	800 165 26	International Dial In:	+44 1452 55 00 00
France	0805 111 340
Italy	800 782 436	Passcode:	646375#
Netherlands	0800 023 4612
Reservation No:	646375
Alternatively a live webcast and a playback facility will be available on the Company's website www.stoltoffshore.com

3

STOLT OFFSHORE S.A. AND SUBSIDIARIES
CONSOLIDATED STATEMENTS OF OPERATIONS
(in thousands, except per share data)

		Unaudited Three Months Ended						Unaudited Nine Months Ended
		August 31, 2002			August 31, 2001			August 31, 2002			August 31, 2001
Net operating revenue		$	368,943		$	365,578		$	996,419		$	838,654
Operating expenses			(371,153	)		(313,261	)		(953,419	)		(762,630	)
Gross (loss)/profit			(2,210	)		52,317			43,000			76,024
Equity in net income of non-consolidated joint ventures			4,013			2,222			9,517			6,923
Administrative and general expenses			(15,292	)		(15,191	)		(51,222	)		(47,485	)
Other operating income/(expense)			5,077			(204	)		5,911			2,170
(Loss)/income from operations			(8,412	)		39,144			7,206			37,632
Non-operating (expense)/income
	Interest expense, net		(4,563	)		(7,162	)		(12,682	)		(22,204	)
	Foreign exchange gain		565			291			528			1,124
(Loss)/income before income taxes and minority interests			(12,410	)		32,273			(4,948	)		16,552
Income tax provision			(5,506	)		(11,165	)		(4,526	)		(16,775	)
(Loss)/income before minority interests			(17,916	)		21,108			(9,474	)		(223	)
Minority interests			717			(3,604	)		(2,657	)		(4,042	)
Net (loss)/income		$	(17,199	)	$	17,504		$	(12,131	)	$	(4,265	)
PER SHARE DATA
Net (loss)/profit per share
	Basic	$	(0.21	)	$	0.20		$	(0.14	)	$	(0.05	)
	Diluted	$	(0.21	)	$	0.20		$	(0.14	)	$	(0.05	)
Weighted average number of Common Shares and Common Share equivalents outstanding
	Basic		83,068			87,225			85,113			87,192
	Diluted		83,068			87,680			85,113			87,192
SELECTED INFORMATION
Capital expenditures		$	20,796		$	17,307		$	39,623		$	59,588
Depreciation and amortization		$	24,575		$	22,282		$	67,927		$	64,203

STOLT OFFSHORE S.A. AND SUBSIDIARIES
CONSOLIDATED BALANCE SHEETS
(in thousands)

				Unaudited August 31, 2002			Unaudited August 31, 2001			Audited November 30, 2001
ASSETS
	Cash and cash equivalents			$	9,037		$	12,780		$	11,670
	Other current assets				485,084			486,443			561,297
	Fixed assets, net of accumulated depreciation				778,631			799,921			779,471
	Other non-current assets				212,912			232,217			207,825
		Total assets		$	1,485,664		$	1,531,361		$	1,560,263
LIABILITIES AND SHAREHOLDERS' EQUITY
	Bank overdrafts			$	8,890		$	20,245		$	5,240
	Current portion of long-term debt and capital lease obligations				40,031			23,999			23,653
	Accounts payable and accrued liabilities				398,356			406,227			465,882
	Long-term debt and capital lease obligations				365,009			325,036			335,026
	Other non-current liabilities				61,229			80,192			70,440
	Shareholders' equity
		Common Shares			140,486			140,457			140,457
		Class B Shares			68,000			68,000			68,000
		Paid-in-surplus			403,076			463,648			463,615
		Retained earnings			37,793			62,375			52,436
		Accumulated other comprehensive loss			(7,225	)		(58,818	)		(64,486	)
		Treasury Shares			(29,981	)		—			—
			Total shareholders' equity		612,149			675,662			660,022
			Total liabilities and shareholders' equity	$	1,485,664		$	1,531,361		$	1,560,263
			Total interest-bearing debt and capital lease obligations, net of cash and cash equivalents and receivables from related parties	$	404,893		$	356,500		$	352,249

STOLT OFFSHORE S.A. AND SUBSIDIARIES
SEGMENTAL ANALYSIS
(in thousands)

        In 1999, the Company adopted SFAS No. 131 "Disclosures about Segments of an Enterprise and Related Information" which changed the way the Company reported information about its operating segments. The tables below show summarized profit and loss information relating to this disclosure. Balance sheet information has not been disclosed as there has not been a material movement in segmental assets since November 30, 2001.

        The Company has seven reportable segments based on geographical regions: Asia Pacific, North America, Norway, SEAME(a), South America, UK and Corporate. Management may from time to time change the segmentation of the business, which will result in a restatement of the figures.

		Asia Pacific			North America			Norway		SEAME(a)			South America		UK			Corporate			Total
For the three months ended August 31, 2002
Net operating revenue — external		$	7,256		$	30,720		$	40,257	$	155,650		$	12,371	$	94,365		$	28,324		$	368,943
Net operating revenue — internal(b)		$	263		$	16,362		$	8,919	$	35,504		$	3,465	$	27,031		$	(571	)	$	—
Income/(loss) from operations		$	794		$	1,435		$	6,929	$	(27,815	)	$	3,804	$	(7,115	)	$	13,556		$	(8,412	)
	Interest expense, net																				$	(4,563	)
	Foreign exchange gain																				$	565
Loss before taxes and minority interests																					$	(12,410	)
For the three months ended August 31, 2001
Net operating revenue — external		$	13,529		$	93,028		$	43,869	$	132,548		$	11,507	$	62,849		$	8,248		$	365,578
Net operating revenue — internal(b)		$	(544	)	$	5,061		$	4,365	$	12,897		$	3,761	$	3,069		$	(5,112	)	$	—
Income/(loss) from operations (c)		$	1,031		$	(4,911	)	$	1,160	$	14,873		$	2,414	$	2,378		$	22,199		$	39,144
	Interest expense, net																				$	(7,162	)
	Foreign exchange gain																				$	291
Income before taxes and minority interests																					$	32,273
For the nine months ended August 31, 2002
Net operating revenue — external		$	19,859		$	154,934		$	79,270	$	455,358		$	38,923	$	159,468		$	88,607		$	996,419
Net operating revenue — internal(b)		$	851		$	42,823		$	19,503	$	66,771		$	9,826	$	46,376		$	3,136		$	—
Income/(loss) from operations		$	110		$	(7,323	)	$	10,847	$	(558	)	$	9,701	$	(9,230	)	$	3,659		$	7,206
	Interest expense, net																				$	(12,682	)
	Foreign exchange gain																				$	528
Loss before taxes and minority interests																					$	(4,948	)
For the nine months ended August 31, 2001
Net operating revenue — external		$	24,526		$	161,199		$	83,172	$	375,423		$	37,765	$	143,078		$	13,491		$	838,654
Net operating revenue — internal (b)		$	(419	)	$	16,456		$	22,633	$	38,550		$	5,609	$	29,279		$	5,054		$	—
(Loss)/income from operations (c)		$	(195	)	$	(6,656	)	$	8,146	$	24,863		$	6,419	$	8,886		$	(3,831	)	$	37,632
	Interest expense, net																				$	(22,204	)
	Foreign exchange gain																				$	1,124
Income before taxes and minority interests																					$	16,552

^(a)

SEAME is defined as Southern Europe, Africa and the Middle East

^(b)

Internal revenues are eliminated on consolidation of the Company's results and are therefore shown in the table to equal to zero

^(c)

Income/(loss) from operations reflects the reclassification of items previously disclosed as "other non-operating income/(expense)'.

        Two customers each individually accounted for more than 10% of the Company's revenue in the quarter and nine months ended August 31, 2002, respectively. The revenue from these customers was $80.9 million for the quarter and $211.1 million for the nine months and was attributable to the Norway and SEAME segments. In the quarter ended August 31, 2001, three customers each individually accounted for more than 10% of the revenue. For the nine months ended August 31, 2001, two customers each individually accounted for more than 10% percent of the revenue. The revenue from these customers was $188.3 million for the quarter and $318.3 million for the nine months ended August 31. These revenues were attributable to the Asia Pacific, North America, Norway, SEAME and UK segments.

QuickLinks

Stolt Offshore S.A. Announces Third Quarter Results And Additional Management Changes
STOLT OFFSHORE S.A. AND SUBSIDIARIES CONSOLIDATED STATEMENTS OF OPERATIONS (in thousands, except per share data)
STOLT OFFSHORE S.A. AND SUBSIDIARIES CONSOLIDATED BALANCE SHEETS (in thousands)
STOLT OFFSHORE S.A. AND SUBSIDIARIES SEGMENTAL ANALYSIS (in thousands)