<PAGE>
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                                 UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
 
                            ------------------------
 
                                   FORM 20-F
 
                    ANNUAL REPORT PURSUANT TO SECTION 13 OR
                  15(D) OF THE SECURITIES EXCHANGE ACT OF 1934
 
                  FOR THE FISCAL YEAR ENDED NOVEMBER 30, 1998
                         COMMISSION FILE NUMBER 0-21742
 
                            ------------------------
 
                            STOLT COMEX SEAWAY S.A.
             (Exact name of Registrant as specified in its charter)
                                   LUXEMBOURG
                (Jurisdiction of incorporation or organization)
                        C/O STOLT COMEX SEAWAY M.S. LTD
                                BUCKSBURN HOUSE
                                   HOWES ROAD
                                   BUCKSBURN
                          ABERDEEN AB21 9RQ, SCOTLAND
                    (Address of principal executive offices)
 
SECURITIES REGISTERED OR TO BE REGISTERED PURSUANT TO SECTION 12(B) OF THE ACT:
                                      None
SECURITIES REGISTERED OR TO BE REGISTERED PURSUANT TO SECTION 12(G) OF THE ACT:
                         Common Shares, $2.00 par value
                        Class A Shares, $2.00 par value
 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:
 
<TABLE>
<S>                                                               <C>
Common Shares, $2.00 par value:.................................  22,365,477*
Class A Shares, $2.00 par value:................................  19,679,987*
Class B Shares, $2.00 par value:................................  34,000,000*
</TABLE>
 
  * The above figures reflect the Class A Share distribution on June 25, 1998.
 
                            ------------------------
 
    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.
 
                                Yes /X/    No / /
 
    Indicate by check mark which financial statement item the registrant has
elected to follow.
 
                            Item 17 / /    Item 18 /X/
 
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<PAGE>
                               TABLE OF CONTENTS
 
<TABLE>
<CAPTION>
                                                                                                             PAGE
                                                                                                             -----
<S>         <C>         <C>                                                                               <C>
PART I
            Item 1.     Description of Business.........................................................           1
                        General.........................................................................           1
                        History.........................................................................           1
                        Business Strategy...............................................................           2
                        Description of Operations.......................................................           2
                        Geographic Distribution.........................................................           4
                        Customers.......................................................................           5
                        Regulation......................................................................           6
                        Competition.....................................................................           6
                        Other Matters...................................................................           6
            Item 2.     Description of Property.........................................................           8
                        Major Assets....................................................................           8
                        Other Properties................................................................          10
            Item 3.     Legal Proceedings...............................................................          11
            Item 4.     Control of Registrant...........................................................          11
            Item 5.     Nature of Trading Market........................................................          12
            Item 6.     Exchange Controls and Other Limitations Affecting Security Holders..............          13
                        Exchange Controls...............................................................          13
                        Limitations Affecting Shareholders..............................................          13
            Item 7.     Taxation........................................................................          14
                        U.S. Taxation...................................................................          14
                        Luxembourg Taxation.............................................................          14
            Item 8.     Selected Financial Data.........................................................          14
                        Dividends.......................................................................          14
            Item 9.     Management's Discussion and Analysis of Financial Condition and Results of                15
                        Operations......................................................................
                        Recent Developments.............................................................          15
                        The Year 2000 Issue.............................................................          15
                        Forward-looking Statements......................................................          16
                        Factors Affecting Revenues and Costs............................................          16
            Item 9A.    Quantitative and Qualitative Disclosures about Market Risk......................          20
            Item 10.    Directors and Officers of Registrant............................................          21
            Item 11.    Compensation of Directors and Officers..........................................          23
                        Profit Sharing Plan.............................................................          23
            Item 12.    Options to Purchase Securities From Registrant or Subsidiaries..................          24
            Item 13.    Interest of Management in Certain Transactions..................................          25
PART III
            Item 15.    Defaults Upon Senior Securities.................................................          26
            Item 16.    Changes in Securities, Changes in Security for Registered Securities and Use of           26
                        Proceeds........................................................................
PART IV
            Item 17.    Financial Statements............................................................          26
            Item 18.    Financial Statements............................................................          26
            Item 19.    Financial Statements and Exhibits...............................................          26
</TABLE>
 
------------------------
 
Note: Omitted items are inapplicable.
<PAGE>
                                     PART I
 
ITEM 1. DESCRIPTION OF BUSINESS
 
GENERAL
 
    Stolt Comex Seaway S.A. ("SCS") is a holding company which through its
subsidiaries is among the leading subsea contractors in the world, providing
technologically sophisticated subsea engineering, flexible and rigid flowline
lay, subsea construction, inspection and maintenance services to its customers
in the offshore oil and gas industry. SCS operates in Europe, the Middle East,
West Africa, Asia Pacific and the Americas.
 
    In this Report, "Company" refers to SCS and, unless the context otherwise
requires, its consolidated subsidiaries. References to Company activities by
years refer to fiscal years ended November 30. SCS was incorporated in
Luxembourg in 1993 as the holding company for all of the Company's activities.
References to matters relating to the Company for periods prior to the
incorporation of SCS in 1993 refer to such matters in respect of the combined
business of Comex Services S.A. ("Comex"), Stolt-Nielsen Seaway A/S ("Seaway"),
and their respective consolidated subsidiaries.
 
    The Company is an indirect subsidiary of Stolt-Nielsen S.A. ("SNSA"), a
Luxembourg company which, through its subsidiaries, is engaged in three
businesses: Transportation Services, Subsea Services and Seafood. As of March
31, 1999 SNSA retains an economic interest of 44.9% and voting rights of 61.6%
in SCS.
 
    The Company's Common Shares and Class A Shares are currently traded on both
the Nasdaq National Market System ("Nasdaq") and on the Oslo Stock Exchange
("OSE").
 
    The registered office of SCS is located at 26, rue Louvigny, Luxembourg and
it is registered in the Companies' Registrar of the Luxembourg District Court
under the designation "R.C. Luxembourg B 43172." The principal executive offices
of the Company are c/o Stolt Comex Seaway M.S. Ltd., Bucksburn House, Howes
Road, Bucksburn, Aberdeen, AB21 9RQ, Scotland, telephone number (44)
1224-718200.
 
HISTORY
 
    The subsea services industry developed as a support service to the oil and
gas industry and has grown as that industry has increasingly relied upon the
development of offshore fields to meet increased demand for oil and gas. The
offshore production of oil began in the Gulf of Mexico in the mid-1960s and, by
the end of the decade, had spread to the more hostile and deeper waters of the
North Sea. Although oil and gas producing companies perform some of their own
subsea construction, maintenance and repair work, subsea services has developed
as a separate industry, principally because of the need to develop new and
advanced technologies, expertise and custom-designed equipment and because of
the oil industry's refocus on its core oil and gas production business.
 
    A publicly-traded company since May 1993, SCS was established through the
merger of the businesses of two leading diving support services companies, Comex
Services S.A. and Stolt-Nielsen Seaway A/S, which were acquired by SNSA in
separate transactions in 1992. At the time of acquisition, Comex was a leading
worldwide subsea services contractor, which pioneered deep water saturation
diving and subsea construction using both manned and unmanned techniques. Seaway
operated principally in the North Sea and pioneered the development and use of
specially designed, technologically sophisticated diving support ships and
remotely operated vehicles ("ROVs") to support operations in hostile deep water
environments.
 
    SCS completed an initial public offering of 6,000,000 Common Shares in May
1993, raising additional share capital of approximately $43 million. During 1997
SCS raised additional share capital of approximately $240 million by means of
two equity offerings. These proceeds are net of offering expenses of $11
million. In March 1997, 8,050,000 Common Shares were sold by the Company and
during November 1997 an additional 4,000,000 Common Shares were sold. Concurrent
with the March offering the Company exchanged debt due to an affiliate of SNSA
for 14,000,000 Class B Shares. Concurrent with the
 
                                       1
<PAGE>
November offering SNSA sold 4,000,000 Common Shares which had been converted
from 8,000,000 Class B Shares.
 
    On January 9, 1998 the Company completed a two-for-one stock split which was
effected by means of a stock dividend distribution. On June 25, 1998 the Company
issued a stock dividend in the form of one new Class A Share for each two Common
Shares. All share data and per share data have been restated to reflect this.
 
    In August 1998, SCS acquired Ceanic Corporation ("Ceanic"), a publicly
traded Houston-based subsea contractor, for approximately $219 million. Ceanic
provides both subsea services and products to the offshore oil and gas industry
in the Gulf of Mexico and inland underwater services and products to domestic
industrial and governmental customers. With Ceanic, SCS took ownership of a
substantial fleet of ships, ROVs, and other related technologies.
 
    The acquisition of Ceanic was strategically important for SCS to access the
growing deep water market for subsea services in the Gulf of Mexico, and to
strengthen the dialogue with Houston-based oil and gas companies with regard to
providing them with subsea services for their worldwide needs. The Ceanic
acquisition provides SCS with a leading position in the traditional Gulf of
Mexico market for subsea services.
 
    In December 1998 SCS acquired the ROV business of Dolphin A/S for
approximately $17 million. This acquisition included 21 ROVs, the majority of
which are on long-term contracts to major oil companies in Norway.
 
BUSINESS STRATEGY
 
    The Company's strategy is to enhance its position as a leading full-service
subsea contractor providing technologically advanced and cost effective
life-of-field subsea services to its customers.
 
    The Company has consistently expanded and upgraded its fleet in order to
provide cost effective solutions to its customers and to enable the development
of offshore fields that otherwise might not be commercially viable. Between 1993
and March 31, 1999, the Company invested $400 million in new technology and
equipment to respond to growing demand in the market, with an additional $47
million committed or planned for the remainder of 1999.
 
    The acquisition of Ceanic has enabled the Company to enter the shallow water
maintenance market in the Gulf of Mexico, a new market for SCS. Through the
Ceanic acquisition, the Company also took over Ceanic's "Big Inch" Marine
Systems subsea pipeline connector business and the "Tarpon Tower" technology.
The Company believes that both of these businesses have considerable growth
potential. The "Big Inch" technology lends itself to our established robotic
skills for deepwater work and the "Tarpon Towers" have become an integral part
of our shallow water field development solutions worldwide.
 
    SCS combines centralized product line profit centers and asset management
with regional management of customer relationships and project support, to
improve the utilization of assets and their allocation to projects to achieve
higher returns, improve risk management, provide superior customer service and
develop and share advanced technical expertise among regions.
 
DESCRIPTION OF OPERATIONS
 
    The Company is one of the largest subsea services contractors in the world,
providing technologically sophisticated subsea engineering, flexible and rigid
flowline lay, subsea construction, inspection, maintenance and repair services
to its customers in the offshore oil and gas industry. SCS develops and applies
innovative and cost efficient subsea techniques that address the evolving
technical needs of oil and gas companies which are increasingly developing oil
and gas fields in deeper and more demanding offshore environments. SCS has
operated in more than 60 countries worldwide and currently operates in over 20
 
                                       2
<PAGE>
countries. The Company's backlog at March 31, 1999 stands at $596 million, of
which $355 million is for 1999. This compares to a backlog at March 31, 1998 of
$517 million, of which $274 million was for 1998.
 
    The Company's services cover all phases of offshore oil and gas operations
from exploration to decommissioning. During the exploration phase, the Company
provides seabed survey and drilling support services. During the development
phase, the Company provides, with partners when appropriate, engineering design,
component procurement, and the installation of subsea equipment, well control
umbilicals, flowlines and production risers. During the production phase, which
may continue for many years, the Company inspects, maintains and repairs
platforms, pipelines, flowlines and subsea equipment. Following the production
phase, the Company provides field decommissioning services including the removal
of offshore structures and subsea equipment.
 
    The Company offers three principal product lines. Field development provides
complete subsea production systems from engineering and design through
procurement and installation of components and the commissioning of completed
systems and installation of rigid and flexible flowlines, small-diameter
pipelines and well control umbilicals. Subsea construction provides pipeline
tie-ins, installation of structures and moorings, hyperbaric welding, piling,
decommissioning, dredging, hot tapping, cold cutting and pipeline stabilization.
Subsea services provides pipeline and flowline survey, construction support,
drilling support and inspection, maintenance and repair.
 
    In addition to its main product lines, the Company offers heavy lift
services through a joint venture company, Seaway Heavy Lifting Limited ("SHL"),
which operates the heavy lift ship, STANISLAV YUDIN, chartered from a subsidiary
of the Company's indirect joint venture partner Lukoil-Kaliningradmorneft Plc.
("LKMN"), a subsidiary of a major Russian oil company, Lukoil.
 
    The remainder of the joint ventures in which the Company has interests have
been entered into on a project-specific basis to enhance the range of services
provided to the customer. In these joint ventures the Company will typically
have interests ranging from 22% to 50%.
 
    The Company operates one of the world's most advanced fleets of subsea
construction and flowline lay ships, from which the majority of SCS's subsea
activities are performed. SCS owns or charters a fleet consisting of four
flexible flowline and umbilical lay ships, one rigid and flexible flowline lay
ship, three construction ships, two survey ships, seven inspection, repair and
maintenance ships, 16 shallow water ships, one heavy lift ship operated through
SHL, 11 lay barges and tugs, 108 ROVs and 13 hardsuits.
 
    Investments in the fleet since 1993 include the acquisition and completion
of the SEAWAY EAGLE, a multi-purpose flowline lay and subsea construction ship,
the conversion of the SEAWAY OSPREY to lay flexible flowlines and flowline
bundles, the acquisition of the SEAWAY FALCON and its conversion to a rigid and
flexible flowline lay ship, the conversion of the SEAWAY CONDOR to a flexible
flowline and umbilical lay ship, the acquisition of the SEAWAY HAWK, a subsea
construction ship and continuous investment in new ROV technology and
construction equipment. SCS also took over the long-term lease on the DISCOVERY,
a multi-purpose subsea construction ship, as part of an asset swap with SubSea
Offshore Limited in 1997.
 
    During the year the Company entered into a long-term charter for the NTL
900, a derrick/lay barge. In addition, the SEAWAY KINGFISHER, a diverless
inspection, repair and maintenance ship, was introduced into the North Sea
market at the end of August 1998.
 
                                       3
<PAGE>
GEOGRAPHIC DISTRIBUTION
 
    The Company's operations are managed through six regional offices: Aberdeen,
Scotland for the U.K. and Southern North Sea; Stavanger, Norway for Norway;
Perth, Australia for Asia Pacific; Marseille, France for Southern Europe, Africa
and the Middle East ("SEAME"); Macae City, Brazil for South America and Houston,
Texas for the Gulf of Mexico.
 
    The following table sets forth the net operating revenue in the principal
areas of operations for the Company's six geographical regions for the periods
indicated:
<TABLE>
<CAPTION>
                                                                                          FOR THE YEARS ENDED
                                                                                  -----------------------------------
<S>                                                                               <C>        <C>            <C>
                                                                                             NOVEMBER 30,
                                                                                    1998         1997         1996
                                                                                  ---------  -------------  ---------
 
<CAPTION>
                                                                                             (IN MILLIONS)
<S>                                                                               <C>        <C>            <C>
U.K.............................................................................  $   333.1    $   172.8    $    95.5
Norway..........................................................................       99.5         90.1        111.6
Asia Pacific....................................................................       37.9         39.6         39.2
SEAME...........................................................................       58.3         75.7         44.6
South America...................................................................       58.5         43.7         14.3
Gulf of Mexico..................................................................       62.5          9.2          8.2
                                                                                  ---------       ------    ---------
Total...........................................................................  $   649.8    $   431.1    $   313.4
                                                                                  ---------       ------    ---------
                                                                                  ---------       ------    ---------
</TABLE>
 
    U.K.
 
    The U.K. region's major clients are oil and gas producing companies and
large offshore engineering and construction companies. The majority of contracts
are short-term in nature with a long-term construction and maintenance contract
for BP Amoco and a long-term construction framework agreement for Arco British
Limited.
 
    Significant projects in the U.K. backlog include the Amerada Hess Triton
engineering, procurement, installation and commissioning ("EPIC") field
development, the Burlington Resources Dalton field development and the Talisman
Energy Orion field development.
 
    NORWAY
 
    The Company's Norwegian business is primarily related to flowline lay,
subsea construction and subsea services, with a customer base consisting of all
of the oil and gas companies operating in Norway. The Company manages its survey
activities for the North Sea from Norway, where it has two long-term survey and
pipeline inspection contracts with Statoil.
 
    The Company also has a long-term contract with Statoil for subsea
construction services which is conducted by a project alliance between the
Company and Brown and Root Energy Services A/S. Other significant contracts in
Norway's backlog include the flowline installation of the Aasgard umbilicals and
service lines for Statoil from 1998 to 2000, the installation of the moorings
for the Esso Jotun FPSO, the Eldfisk riser project and the Maersk caisson
installation.
 
    ASIA PACIFIC
 
    The Asia Pacific region is characterized by long distances between areas of
offshore oil operations and from other areas of the world with subsea
development activities. The Company is active in ROV work and drilling support
in this region. In Indonesia, the Company's operations are performed through a
subsidiary, PT Komaritim, which carries out shallow water pipelay and
construction work. The Company has entered into a long-term charter for the NTL
900 derrick/lay barge which will enhance the Company's capabilities in pipelay,
heavy lift and deeper water work around the Asia Pacific region. A new pipelay
barge has also been built for the Indonesia shallow water market.
 
                                       4
<PAGE>
    Significant contracts in the backlog include the Total Tunu phase 6 pipelay
contract and the Peciko contract for Saipem in Indonesia.
 
    SEAME
 
    The majority of the business conducted by the SEAME region is offshore from
West Africa and the Middle East. The significant contract in the backlog is the
Elf Exploration Angola Girassol contract. This contract was awarded to SCS and
its project partners, Bouygues Offshore and ETPM. The Company has a one-third or
$138 million share of this subsea EPIC contract. This is the first
ultra-deepwater field development off West Africa, a significant milestone in
the development of technology for installations of this type in extreme water
depths.
 
    SOUTH AMERICA
 
    The majority of operations in South America are located in Brazil which
currently operates as a single customer market controlled by Petrobras, the
Brazilian state oil company. Brazil is now in the process of opening its
offshore oil and gas fields to foreign operators who will finance the growth of
Brazilian offshore oil production by means of production sharing contracts. The
Company believes the introduction of foreign operators to Brazil will double the
demand for subsea contractor services within four years.
 
    Current production in Brazil occurs at water depths down to 800 meters. The
Brazilian market contains a number of potentially large field developments which
are located in deep water (between 700 and 1,830 meters), and will require
extensive use of diverless subsea construction techniques. The Company believes
it is well positioned to capitalize upon its expertise in these techniques.
 
    The Company currently has a three-year contract for the SEAWAY OSPREY with
Petrobras through September 1999, with an optional one-year extension, and a
four-year contract with Petrobras which started in May 1997 for the SEAWAY
HARRIER. These contracts are for flowline lay, diving support and ROV services.
The Company also operates a number of ROVs to provide construction and drilling
support services, usually under long-term contracts.
 
    GULF OF MEXICO
 
    The Company intends to capitalize on the acquisition of the Ceanic
Corporation, now renamed Stolt Comex Seaway Inc., to expand its presence in the
Gulf of Mexico by introducing established SCS deepwater technology and
sophisticated deepwater construction ships during 1999. Houston is the base from
which U.S. oil companies conduct their worldwide operations. The new SCS
organization in Houston will be the marketing point of contact for worldwide
operations for U.S. based customers. The SEAWAY HAWK, purchased in May 1997,
started a two-year contract offshore from Mexico in April 1998. The Company also
relocated the SEAWAY CONDOR to the Gulf of Mexico in December 1998. These
relocations will bring the number of dynamically positioned ships in the region
to eight.
 
    A significant number of contracts in this region are short-term construction
and repair and maintenance contracts.
 
CUSTOMERS
 
    In 1998, the Company had 88 customers worldwide, of which 46% were major
national and international oil and gas companies. The level of construction
services required by any particular customer depends on the size of that
customer's capital expenditure budget devoted to construction plans in a
particular year. Consequently, customers that account for a significant portion
of contract revenue in one fiscal year may represent an immaterial portion of
contract revenue in subsequent fiscal years. One customer, Amerada Hess,
accounted for more than 22% of the Company's net operating revenue and the seven
largest customers were responsible for approximately 60% of the Company's net
operating revenue in 1998.
 
                                       5
<PAGE>
REGULATION
 
    The Company's businesses are subject to international conventions and
governmental regulations, which strictly regulate various aspects of its
operations. In addition, SCS is required by various governmental and other
regulatory agencies to obtain certain permits, licenses and certificates with
respect to its equipment and operations. The kind of permits, licenses and
certificates required in the operations of the Company depend upon a number of
factors. The Company believes that it has or can readily obtain all permits,
licenses and certificates necessary to conduct its operations. Some countries
require that the Company enter into a joint venture or similar business
arrangement with local individuals or businesses in order to conduct business in
such countries.
 
    The Company's operations are affected from time to time and to varying
degrees by political developments and federal and local laws and regulations. In
particular, oil and gas production, operations and economics are affected by
price control, tax and other laws relating to the petroleum industry, by changes
in such laws and by constantly changing administrative regulations. Such
developments directly or indirectly may affect the Company's operations and
those of its customers.
 
COMPETITION
 
    The subsea contracting business is highly competitive. The consolidation in
the offshore oil and gas services industry in the last few years has resulted in
fewer but more substantial competitors. Although the Company believes customers
consider, among other things, the availability and technical capabilities of
equipment and personnel, efficiency, condition of equipment, safety record and
reputation, price competition is the primary factor in determining which
qualified contractor with available equipment will be awarded a contract. SCS's
ships are specialized and have few alternative uses and, because of their nature
and the environment in which they work, have relatively high maintenance costs
whether or not operating. Because these costs are essentially fixed, and in
order to avoid additional expenses associated with temporarily idling its ships,
the Company may from time to time be required to bid its ships in projects at
lower margins depending on the prevailing contractual rates in a given region.
 
    SCS believes that it is one of only three companies capable of providing the
full range of subsea services on a worldwide basis in the major offshore oil and
gas producing regions. Competition across all main product lines is limited to
SCS and two competitors, Coflexip Stena Offshore and Rockwater, a subsidiary of
Brown and Root, itself a division of Halliburton. The Company is subject to
intense competition from these offshore contractors. In certain geographical
regions, and in certain product lines, SCS also competes with J. Ray McDermott
Inc., Global Industries Limited and DSND. The Company also faces substantial
competition from smaller regional competitors and less integrated providers of
subsea services.
 
OTHER MATTERS
 
    CO-OPERATION ARRANGEMENTS
 
    In certain project specific situations, the Company has entered into
alliances with its customers, engineering companies and other subsea services
providers. The Company has an alliance with NKT Cables, which manufactures
flexible flowlines and risers.
 
    EMPLOYEES
 
    The Company's workforce varies based on the Company's workload at any
particular time. As of March 31, 1999, the Company had approximately 4,000
employees. A significant number of the Company's offshore employees are
represented by labor unions. As part of normal business, a number of union
agreements come up for annual renegotiation in 1999. The Company believes that
it maintains a good relationship with its employees and their unions. In
addition, many workers are hired on a contract basis and are available on short
notice.
 
                                       6
<PAGE>
    SAFETY AND QUALITY ASSURANCE
 
    The Company maintains a stringent quality assurance program in accordance
with ISO 9001 which encompasses all areas of its operations. Each of the
Company's regional operations has dedicated safety and quality assurance staff
who are responsible for overseeing the projects in that particular region. In
addition, a quality assurance manager located in Aberdeen, Scotland formulates
corporate policies with respect to quality assurance and oversees the
implementation and enforcement of such policies on a Company-wide basis.
 
    RISKS AND INSURANCE
 
    The Company's operations are subject to all the risks normally associated
with offshore development and production and could result in damage to or loss
of property, suspension of operations or injury or death to personnel or third
parties. The Company insures its assets at levels which management believes
reflect their current market value. Such assets include all capital items, such
as ships, major equipment and land-based property. The only assets not insured
are those where the cost of such insurance would be disproportionate to their
value. The Company believes its insurance should protect it against, among other
things, the cost of replacing its ships as a result of total or constructive
total loss.
 
    The Company's operations are conducted in hazardous environments where
accidents involving catastrophic damage or loss of life could result, and
litigation arising from such an event may result in the Company being named a
defendant in lawsuits asserting large claims. The Company insures itself for
liability arising from its operations, both onshore and offshore, including loss
of or damage to third-party property, death or injury to employees or third
parties, statutory workers compensation protection and pollution. Although there
can be no assurance that the amount of insurance carried by the Company is
sufficient to protect it fully in all events, all such insurance is carried at
levels of coverage and deductibles that the Company considers financially
prudent. A successful liability claim for which the Company is underinsured or
uninsured could have a material adverse effect on the Company.
 
    INSPECTION BY A CLASSIFICATION SOCIETY AND DRYDOCKING
 
    The hull and machinery (including diving equipment) of most of the SCS ships
must be "classed" by a classification society authorized by its country of
registry. The classification society certifies that the ship is safe and
seaworthy in accordance with the classification rules as well as with applicable
rules and regulations of the country of registry of the ship and the
international conventions of which that country is a member. Certain of the SCS
ships are not required to be classed, but do comply with applicable regulations.
 
    Each classed ship is inspected by a surveyor of the classification society.
A visual inspection is carried out annually to ascertain the general condition
of the ship or relevant items. Intermediate surveys are carried out at the
second or third annual survey. This survey includes a visual inspection of the
hull structure, machinery and electrical installations and equipment. Renewal
surveys which involve a major inspection of the hull structure, machinery
installations and equipment are carried out at five-yearly intervals. A classed
ship is also required to be drydocked every 30 to 36 months for inspection of
the underwater parts of the ship. As a general policy, the Company drydocks its
classed ships every second year during the winter off-season. Should any defect
be found, the classification society surveyor will issue its report as to
appropriate repairs which must be made by the shipowner within the time limit
prescribed. Insurance underwriters make it a condition of insurance coverage
that a classed ship be "in class," and all of the Company's major classed ships
currently meet that condition.
 
                                       7
<PAGE>
    The U.S. flagged SCS ships that are U.S. Coast Guard inspected but not
classed are drydocked twice in each five year cycle. The intermediate drydocking
is due between the end of the second and third years of the cycle. The U.S.
flagged Load Line only ships as well as the un-classed Panama and Honduras
flagged ships are drydocked according to the same schedule for Condition Surveys
as required by the respective national Load Line regulations. The annual topside
safety and equipment surveys are very similar to and parallel the traditional
class surveys.
 
ITEM 2. DESCRIPTION OF PROPERTY
 
MAJOR ASSETS
 
    The Company operates one of the world's most advanced fleets of subsea
construction support and flowline lay ships from which the majority of SCS's
subsea activities are performed. The following table describes the Company's
major assets, as of March 31, 1999:
 
<TABLE>
<CAPTION>
                                                                       YEAR BUILT/                    LENGTH          OWNED/
NAME                                        CAPABILITIES              MAJOR UPGRADE       ROVS       (METERS)       CHARTERED
--------------------------------  --------------------------------  -----------------  -----------  -----------  ----------------
<S>                               <C>                               <C>                <C>          <C>          <C>
 
FLOWLINE LAY SHIPS
SEAWAY EAGLE....................  Flexible flowline lay, multi-
                                  purpose subsea construction       1997                        2          140   Owned(1)
SEAWAY CONDOR...................  Flexible flowline and umbilical
                                  lay, module handling system,
                                  trenching                         1982/1994                   2          101   Owned(1)
SEAWAY OSPREY...................  Flexible flowline and umbilical
                                  lay, accepts coiled tubing,
                                  straightener for tubing, stern
                                  roller                            1984/1992                   2          102   Owned(1)
DISCOVERY.......................  Flexible flowline lay, subsea
                                  construction                      1990                        1          120   Chartered(2)
SEAWAY FALCON...................  Rigid and flexible flowline and
                                  umbilical lay                     1976/1995/1997              2          162   Owned(1)
CONSTRUCTION SHIPS
SEAWAY HARRIER..................  Subsea construction               1985                        1           84   Owned(1)
SEAWAY PELICAN..................  Subsea construction               1986/1990                   1           94   Chartered(3)
SEAWAY HAWK.....................  Subsea construction               1978                       --           94   Owned(1)
 
SURVEY / INSPECTION, REPAIR AND
  MAINTENANCE SHIPS
TOISA PUMA......................  Diving support, light
                                  construction                      1985                       --           77   Chartered(4)
SEAWAY SURVEYOR.................  Survey                            1987/1991                   2           66   Chartered(5)
SEAWAY COMMANDER................  Survey                            1982/1988                   2           75   Chartered(6)
SEAWAY KINGFISHER...............  Diverless inspection, repair and
                                  maintenance                       1990/1998                   2           90   Chartered(7)
SEAWAY INVINCIBLE...............  ROV support, subsea construction  1971                       --           70   Chartered(8)
SEAWAY LEGEND...................  ROV and hardsuit diving support,
                                  subsea construction               1985/1998                   2           64   Owned(1)
</TABLE>
 
                                       8
<PAGE>
<TABLE>
<CAPTION>
                                                                       YEAR BUILT/                    LENGTH          OWNED/
NAME                                        CAPABILITIES              MAJOR UPGRADE       ROVS       (METERS)       CHARTERED
--------------------------------  --------------------------------  -----------------  -----------  -----------  ----------------
<S>                               <C>                               <C>                <C>          <C>          <C>
CEANIC ROVER....................  ROV support, subsea construction  1966/1991                  --           64   Chartered(9)
AMERICAN DEFENDER...............  ROV and hardsuit diving support,
                                  subsea construction               1976                        1           67   Owned(1)
AMERICAN PIONEER................  ROV and hardsuit diving support,
                                  subsea construction               1966/1996                   1           63   Owned(1)
SHALLOW WATER FLEET
AMERICAN ENDEAVOR...............  Utility tug, ROV support          1962                       --           19   Owned
AMERICAN PATRIOT................  Four-point anchor system, 40-ton
                                  crane                             1962/1997                  --           50   Owned(1)
AMERICAN CONSTITUTION...........  Four-point anchor system,
                                  saturation diving, moonpool       1997                       --           56   Owned(1)
AMERICAN DIVER..................  Diving support                    1996                       --           34   Owned
AMERICAN INDEPENDENCE...........  Four-point anchor system          1996                       --           47   Owned(1)
AMERICAN LIBERTY................  Four-point anchor system          1996                       --           35   Owned
AMERICAN RECOVERY...............  Tug, diving support               1965/1995                  --           43   Owned(1)
AMERICAN SCOUT..................  Diving support                    1978                       --           34   Owned
AMERICAN SPIRIT.................  Four-point anchor system          1961/1996                  --           36   Owned
AMERICAN STAR...................  Four-point anchor system,
                                  saturation diving                 1967/1998                  --           47   Owned(1)
AMERICAN TRIUMPH................  Four-point anchor system          1965/1997                  --           48   Owned(1)
AMERICAN VICTORY................  Four-point anchor system          1976/1997                  --           48   Owned(1)
PIPELINE OBSERVER...............  Diving support                    1982                       --           28   Owned
PIPELINE SURVEYOR...............  Diving support                    1965/1996                  --           34   Owned
AMERICAN EAGLE..................  Four-point anchor system          1996                       --           44   Owned(1)
AMERICAN PRIDE..................  Four-point anchor system          1977/1992                  --           51   Owned(1)
HEAVY LIFT SHIP / LAY BARGES /
  TUGS / OTHER
STANISLAV YUDIN.................  Heavy lift, 2,500-ton crane       1985                       --          183   Chartered(10)
NTL 900 (NAN TIAN LONG).........  Derrick lay barge                 1992                       --          100   Chartered(11)
ANNETTE.........................  Pipelay barge, marine
                                  construction                      1989/1997                  --           61   Owned
ARWANA..........................  Pipelay barge                     1998                       --           70   Owned
APM 205.........................  Barge                             1966/1997                  --           61   Owned
JASAMARINE V (EX SIN THAI HIN     Flat top barge fitted out for
  IV)...........................  inshore diving/construction       1978                       --           55   Owned
BULDRA..........................  Work barge, shallow water diving
                                  operations                        1977                       --           25   Owned
GOLEK...........................  Transport barge                   1983/1992                  --           46   Owned
DE ZHONG........................  Offshore tug, supply ship         1997                       --           64   Chartered(11)
POLKA...........................  River tug and anchor handler      1971                       --           12   Owned
KAREGINA........................  Push boat                         1979                       --            8   Owned
MINDY ANN.......................  Push boat                         1986                       --            8   Owned
</TABLE>
 
                                       9
<PAGE>
------------------------
 
(1) Subject to mortgage under the Company's current credit facilities.
 
(2) Chartered from Friary Ocean Surveyor NV through September 2002, with options
    to extend through 2011 and with options to purchase.
 
(3) Chartered from DSND Shipping AS through December 1999.
 
(4) Chartered from Toisa Ltd. through December 2000, with options to extend
    through 2001.
 
(5) Chartered from DSND Chartering I KS through December 1999.
 
(6) Chartered from DSND Chartering I KS through December 1999, with options to
    extend through 2002.
 
(7) Chartered from Kingfisher DA in which the Company has a 50% ownership, for
    five years starting in 1998, with options to extend through December 2013
    and with options to purchase.
 
(8) Chartered from Tidewater Inc. through September 2001 with option to
    purchase.
 
(9) Chartered from Tidewater Inc. through July 2001 with option to purchase.
 
(10) Chartered to SHL by a subsidiary of the ship's owner, LKMN, through October
    2001 with a possibility for extensions.
 
(11) Chartered from Guangzhou Salvage Co., Ltd through October 2000 with options
    to extend through 2003.
 
OTHER PROPERTIES
 
    As of March 31, 1999, SCS owns or holds under long-term leases real estate
property as described below:
 
<TABLE>
<CAPTION>
                                                                                  WORK OR STORAGE
                                                                 OFFICE SPACE      SPACE OR LAND
                                                                (SQUARE METERS)   (SQUARE METERS)       STATUS
                                                               -----------------  ---------------  -----------------
<S>                                                            <C>                <C>              <C>
Aberdeen, Scotland...........................................          7,761           103,369     Owned/Leased
Baku, Azerbaijan.............................................             66                --     Leased
Buenos Aires, Argentina......................................            100                --     Leased
Columbus, Ohio...............................................            279             8,614     Leased
Dhahran, Saudi Arabia........................................            330               750     Leased
Dundee, Scotland.............................................             --             8,234     Leased
Haugesund, Norway (1)........................................          2,570            22,860     Owned/Leased
Houston, Texas...............................................          4,208            15,489     Leased
Jakarta, Indonesia...........................................            915               601     Leased
Lagos, Nigeria...............................................            200                --     Leased
Luanda, Angola...............................................             53               690     Leased
Macae City, Brazil...........................................          1,285             3,685     Owned/Leased
Marseille, France............................................          1,005               416     Leased
New Orleans, Louisiana.......................................            305            56,658     Owned
Oxnard, California...........................................            929             6,643     Leased
Perth, Australia.............................................          1,783             2,233     Leased
Port Gentil, Gabon...........................................            305             5,070     Leased
Port Harcourt, Nigeria.......................................            400               300     Leased
Port of Fourchon, Louisiana..................................            650            74,240     Leased
Port of Iberia, Louisiana....................................          1,796            95,688     Owned
Rio de Janeiro, Brazil.......................................            295                --     Leased
Singapore....................................................            369             1,383     Leased
Stavanger, Norway............................................          3,346               100     Leased
Vancouver, Canada............................................          1,161               785     Leased
</TABLE>
 
------------------------
 
(1) Owned subject to mortgage
 
                                       10
<PAGE>
ITEM 3. LEGAL PROCEEDINGS
 
    The Swiss Court of Insurance "Tribunal Federal des Assurances" entered a
judgement on April 29, 1992 against Sogexpat S.A. ("Sogexpat"), a subsidiary of
the Company, in litigation brought by a Swiss governmental entity claiming
payment of social security contributions in arrears. During the year ended
November 30, 1993, the Company wound up Sogexpat and transferred the employees
to other Group companies. The French government has investigated Stolt Comex
Seaway S.A. of France alleging violations of French labor and social security
legislation, which has resulted during 1998 in a condemnation by the French
Supreme Court of Stolt Comex Seaway S.A. of France and two of its former
directors. In addition, a number of former and present employees have started
civil proceedings against certain subsidiaries of the Company alleging loss of
employment and social security benefits. Some of the proceedings have recently
commenced while some have already resulted in court decisions. One such decision
has been appealed to the French Supreme Court. While the Company believes that
its subsidiaries have meritorious defenses in these cases, there can be no
certainty as to the number of claims which may be brought or the amount for
which the Company may eventually be liable with respect thereto. Comex S.A., a
former shareholder of Comex Services S.A. ("Comex"), in an agreement with SNSA
executed on June 5, 1992 for the sale of Comex, agreed to indemnify the Company
with respect to certain aspects of the foregoing. There can be no assurance,
however, as to the amount which the Company may ultimately recover from Comex
S.A. pursuant to such indemnity.
 
    Coflexip S.A. commenced legal proceedings in the Patents Court, Chancery
Division of the High Court of Justice in the U.K. against three subsidiaries of
the Company claiming infringement of a certain patent relating to flexible
flowline laying technology. In holdings on January 22, 1999 and January 29,
1999, the Court found the disputed patent valid. The Company has appealed. The
Company has provided in the November 30, 1998 financial statements an amount to
cover the estimated liability for Coflexip S.A.'s legal costs resulting from the
litigation. No provision has been made for damages. The extent of the liability
for damages, if any, to Coflexip S.A. for patent infringement in the U.K. is
unknown at this time.
 
    The Company is a party to various other legal proceedings arising in the
ordinary course of business.
 
    The Company believes that such legal proceedings will not have a material
effect on the Company's business or financial condition.
 
ITEM 4. CONTROL OF REGISTRANT
 
    Except as set forth below, SCS is not, directly or indirectly, owned by
another corporation or by any government. There are no arrangements known to the
Company, the operation of which may at a subsequent date result in a change in
control of SCS.
 
    Set forth below is information concerning the share ownership of all persons
who owned beneficially 10% or more of the Common Share equivalents, and the
beneficial ownership of all Directors and persons employed by the Company's
subsidiaries who perform executive and administrative functions for the
Company's combined businesses, as a group, as of March 31, 1999:
<TABLE>
<CAPTION>
                                 NUMBER OF                     NUMBER OF                     NUMBER OF
                                  COMMON                        CLASS A                       CLASS B
NAME OF BENEFICIAL OWNER OR       SHARES       PERCENTAGE       SHARES       PERCENTAGE       SHARES       PERCENTAGE
IDENTITY OF GROUP                  OWNED        OF CLASS         OWNED        OF CLASS         OWNED        OF CLASS
------------------------------  -----------  ---------------  -----------  ---------------  -----------  ---------------
<S>                             <C>          <C>              <C>          <C>              <C>          <C>
Stolt-Nielsen Transportation
  Group Ltd ("SNTG")..........     700,000           3.13%     8,800,000          44.72%     34,000,000           100%
Directors and officers as a
  group (19 persons)..........     111,350           0.50%       145,900           0.74%             --            --
 
<CAPTION>
                                 PERCENTAGE OF
                                 ECONOMICALLY
NAME OF BENEFICIAL OWNER OR       EQUIVALENT
IDENTITY OF GROUP                SHARES OWNED
------------------------------  ---------------
<S>                             <C>
Stolt-Nielsen Transportation
  Group Ltd ("SNTG")..........         44.88%
Directors and officers as a
  group (19 persons)..........          0.44%
</TABLE>
 
------------------------
 
(1) SNTG owns 34,000,000 Class B Shares, constituting 100% of that class. Each
    Class B Share represents one-half of the economic interest of one Common
    Share (with dividend and liquidation rights equivalent to one-half of a
    Common Share) and is convertible into Common Shares on a two-for-one basis.
    If SNSA or its affiliates dispose of Class B Shares to a third party, such
    Class B Shares automatically convert into Common Shares on such two-for-one
    basis.
 
                                       11
<PAGE>
    SNSA is the 100% owner of SNTG. Fiducia Ltd., a company owned by trusts of
which the Stolt-Nielsen family are beneficiaries, owns approximately 61% of the
outstanding Common Shares of SNSA. Jacob Stolt-Nielsen, owns all of the
Founder's Shares of SNSA. The Common Shares owned by Fiducia Ltd. represent
approximately 48.5% of SNSA's outstanding voting securities and the Founder's
Shares owned by Mr. Stolt-Nielsen represent approximately 21% of SNSA's
outstanding voting securities. The Common Shares of SNSA are traded on Nasdaq
and the Oslo Stock Exchange.
 
ITEM 5. NATURE OF TRADING MARKET
 
    SCS's Common Shares are primarily traded on Nasdaq under the symbol "SCSWF".
The Common Shares are also listed for trading on the Oslo Stock Exchange under
the symbol "SCS". SCS's Class A Shares are listed for trading on Nasdaq as
American Depositary Shares ("ADSs"), each of which represents one Class A Share,
under the symbol "SCSAY" and on the Oslo Stock Exchange under the symbol "SCSA".
Trading in the Class A Shares and ADSs commenced in June 1998.
 
    The following table sets forth, for the fiscal periods indicated, the range
of high and low closing sale prices for the Common Shares and the Class A
Shares, in each case to reflect the two-for-one stock split completed on January
29, 1998 and the Class A Share distribution made on June 25, 1998:
 
<TABLE>
<CAPTION>
                                                                            HIGH        LOW
                                                                          ---------  ---------
<S>                                                                       <C>        <C>
NASDAQ
COMMON SHARES
1998
1st Quarter.............................................................  $  18.016  $  12.625
2nd Quarter.............................................................     24.422     14.422
3rd Quarter.............................................................     20.344      7.875
4th Quarter.............................................................     13.500      8.125
1997
1st Quarter.............................................................  $   6.594  $   4.953
2nd Quarter.............................................................      7.734      5.875
3rd Quarter.............................................................     17.797      7.547
4th Quarter.............................................................     22.141     16.391
 
CLASS A SHARES
1998
1st Quarter.............................................................         --         --
2nd Quarter.............................................................         --         --
3rd Quarter.............................................................  $  18.500  $   5.688
4th Quarter.............................................................     11.938      6.500
 
OSLO STOCK EXCHANGE (NORWEGIAN KRONER)
COMMON SHARES
1998
1st Quarter.............................................................     134.73      94.05
2nd Quarter.............................................................     178.09     115.39
3rd Quarter.............................................................     154.00      67.00
4th Quarter.............................................................     101.00      61.00
</TABLE>
 
                                       12
<PAGE>
<TABLE>
<CAPTION>
                                                                            HIGH        LOW
                                                                          ---------  ---------
<S>                                                                       <C>        <C>
1997
1st Quarter.............................................................         --         --
2nd Quarter.............................................................         --         --
3rd Quarter.............................................................     126.73      57.36
4th Quarter.............................................................     181.76     119.56
 
CLASS A SHARES
1998
1st Quarter.............................................................         --         --
2nd Quarter.............................................................         --         --
3rd Quarter.............................................................     143.50      45.00
4th Quarter.............................................................      83.00      45.30
</TABLE>
 
    As of March 1, 1999 (the record date for voting at the Annual General
Meeting), 22,361,280 Common Shares, representing 99.98% of the outstanding
Common Shares, were registered in the names of 39 shareholders having U.S.
addresses (although some of such shares may be held on behalf of non-U.S.
persons). The Common Shares were held by a total of 44 shareholders of record.
Based on communications with banks and securities dealers who hold the Common
Shares in street name for individuals, the Company estimates that the number of
beneficial owners of the Common Shares exceeds 3,000.
 
    As of March 1, 1999, approximately 5,389,336 Common Shares were registered
in the names of 507 shareholders in the Norwegian Verdipapirsentralen ("VPS")
system in Norway. The registration of Common Shares in the VPS system is a
"sub-registrar" arrangement, effected through a U.S. nominee shareholder, so
that the total number of Common Shares in the VPS system is also included in the
total number of Common Shares in the preceding paragraph.
 
    As of March 1, 1999, there were a total of 10,354,574 ADSs of which
10,351,438 were registered in the names of 24 shareholders having U.S. addresses
(although some of such ADSs may be held on behalf of non-U.S. persons). Based on
communications with banks and security dealers who hold SCS's ADSs in street
name for individuals, the Company estimates that the number of beneficial owners
of ADSs exceeds 2,000. As of such date, the ADSs represented 52.61% of the
outstanding Class A Shares of SCS.
 
    All of the Class A Shares (including ADSs) are registered in the VPS system
in Norway. As of March 1, 1999, excluding the Class A Shares held represented by
ADSs and Class A Shares held by SNTG, it is estimated that the free float of
Class A Shares traded on the Oslo Stock Exchange is 825,413 shares registered in
the names of 193 shareholders.
 
ITEM 6. EXCHANGE CONTROLS AND OTHER LIMITATIONS AFFECTING SECURITY HOLDERS
 
EXCHANGE CONTROLS
 
    SCS has been advised by Elvinger, Hoss & Prussen, Luxembourg counsel to the
Company, that at the present time there are no exchange controls in existence in
Luxembourg which would impact the Company's operations or affect the Company's
ability to pay dividends to non-resident shareholders.
 
LIMITATIONS AFFECTING SHAREHOLDERS
 
    The Company's Articles provide restrictions on the shareholdings of certain
"U.S. Persons." Persons includes any individual, firm, corporation or other
entity, and certain associates and affiliates thereof. The Articles provide that
no one U.S. Person (including any Person who is a citizen or resident of the
U.S., a corporation organized under the laws of the U.S. or any State thereof, a
corporation organized under the laws of any other jurisdiction whose shares are
owned by U.S. Persons, a partnership organized under the
 
                                       13
<PAGE>
laws of any State of the U.S., and certain trusts and estates) may own, directly
or indirectly, more than 9.9% of the Company's total outstanding shares at any
particular time.
 
    In addition, the Board is authorized to restrict, reduce or prevent the
ownership of the Company's shares if it appears to the Board that such ownership
may threaten the Company with "imminent and grave damage." Luxembourg company
law does not provide a specific definition of imminent and grave damage, but
instead leaves the interpretation of the phrase within the Board's discretion.
The Company has been advised by its Luxembourg counsel, Elvinger, Hoss &
Prussen, that there are no Luxembourg judicial interpretations of the phrase,
but that situations involving hostile takeovers, adverse tax consequences to the
Company or governmental sanctions are likely to be among the situations covered
by such phrase.
 
    In order to enforce the foregoing restrictions, the Articles empower the
Board to take certain remedial action including causing the Company: (i) to
decline to register any prohibited transfer; (ii) to decline to recognize any
vote of a shareholder precluded from holding shares; (iii) to require any
shareholder on the Company's Register of Shareholders or any prospective
shareholder to provide information to determine whether such person is precluded
from holding shares and (iv) upon the issuance of a notice, to require the sale
of shares to the Company at the lesser of (A) the amount paid for the shares if
acquired within the twelve months immediately preceding the date of the notice,
and (B) the last quoted sale price for the shares on the day immediately
preceding the day on which the notice is served (provided that the Board may in
its discretion pay the amount calculated under (B) in situations where (A) would
otherwise apply and result in a lower purchase price, if the Board determines it
equitable after taking into account specified factors); and to remove the name
of any shareholder from the Register of Shareholders immediately after the close
of business on the day the notice is issued and payment is made available. The
foregoing defensive measures may have the effect of making more difficult a
merger involving the Company, or a tender offer, open-market purchase program or
other purchase of the Company's shares, in circumstances that could give
shareholders the opportunity to realize a premium over the then prevailing
market price for their shares.
 
    There are no limitations currently imposed by Luxembourg law on the rights
of non-resident SCS shareholders to hold or vote their shares.
 
ITEM 7. TAXATION
 
U.S. TAXATION
 
    U.S. corporations, citizens and residents will be subject to U.S. income
taxation on dividends and other distributions paid by SCS and on any gains
derived from the sale of SCS shares.
 
LUXEMBOURG TAXATION
 
    Other than certain former Luxembourg residents, current Luxembourg residents
and those non-residents who maintain a permanent establishment in Luxembourg
with which the holding of SCS Common Shares is connected, SCS shareholders are
not subject to taxation in Luxembourg.
 
ITEM 8. SELECTED FINANCIAL DATA
 
    The information under the caption "Selected Consolidated Financial Data" on
page 25 of the Company's 1998 Annual Report filed with the Securities and
Exchange Commission on Form 6-K is incorporated herein by reference.
 
DIVIDENDS
 
    The Company has made no cash dividend payments since going public in May
1993.
 
                                       14
<PAGE>
ITEM 9. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS
  OF OPERATIONS
 
    The information included under the caption "Management's Discussion and
Analysis of Results of Operations and Financial Condition" on pages 17 through
24 of the Company's 1998 Annual Report filed with the Commission on Form 6-K is
incorporated herein by reference.
 
RECENT DEVELOPMENTS
 
    For the first quarter of 1999, SCS reported a net income of $0.6 million on
net operating revenue of $145.1 million. This compares with a net income of $0.9
million, before the cumulative effect of a change in accounting policy, on net
operating revenue of $92.4 million for the same period in 1998. The results for
the first quarter of 1998 have been restated to reflect the change in drydocking
accounting policy that occurred in the third quarter of 1998. Net income in the
first quarter of 1998 after the effect of the change in accounting policy for
drydocking was $4.0 million.
 
    On December 9, 1998, the Company acquired the remotely operated vehicle
business of Dolphin A/S in a cash transaction for $16.9 million.
 
    In March 1999 the Company acquired the diving division of J. Ray McDermott
Inc. in the Gulf of Mexico and is now providing all diving and related subsea
services to J. Ray McDermott Inc. in this region for a five-year period under an
exclusive agreement.
 
    Subsequent to November 30, 1998, the Company reached agreement for a new
credit facility with Den norske Bank ASA, Bank of America NT & SA, Midland Bank
plc, and ASKL-CGER Bank nv/sa. This new facility is in the form of a five year
revolving credit line. The initial available amount is $150 million which will
be reduced by $12.5 million semi annually leaving $37.5 million due at maturity.
This facility will be used to repay the long-term debt due to SNSA of $150
million.
 
THE YEAR 2000 ISSUE
 
    The Company has established a company-wide initiative to identify, evaluate
and address Year 2000 issues. Beginning in 1997 the Company's Year 2000 effort
has encompassed five main areas; asset integrity, information technology,
infrastructure, business systems and commercial integrity, and is split into
five main phases. These phases, the first three of which are largely complete,
are: an awareness program for the Company's staff, a complete inventory of the
issues, development of an action plan, testing and redevelopment of systems and
the development of a business contingency plan. In addition the project includes
a review of the Year 2000 compliance efforts of key suppliers, customers and
other principal business partners.
 
    Work is progressing on the testing and redevelopment phase of the project
and this is planned to be substantially complete by June 1999 for all those
areas assessed to be of high or medium impact to the business. The Company's
ability to meet that target is dependent on a variety of factors including the
timely provision of necessary upgrades and notifications by suppliers. In
addition the Company has no method of ensuring that third parties who supply
essential services such as utilities will convert their critical systems and
processes in a timely manner. Failure or delay by any of these parties could
significantly disrupt the business. However a supplier compliance program has
been established and the Company is working with its key suppliers to minimize
such risks.
 
    It is currently estimated that the Company will incur approximately $0.6
million of expenses through 2000 in connection with the efforts on Year 2000
issues. At March 31, 1999 the Company had incurred $0.2 million. The timing of
the expenses may vary and are not necessarily an indication of the progress to
date on the project.
 
                                       15
<PAGE>
    The Company has started contingency planning for critical operational areas
that may be affected by the Year 2000 issue and expects to have a full plan in
place by June 1999. This will include contingency plans which may be required
should any third parties fail to achieve Year 2000 compliance.
 
    While the Company believes its efforts to address the Year 2000 issue will
be successful in avoiding any material adverse effect on the Company's
operations or functional condition, it recognizes that failing to resolve Year
2000 issues on a timely basis would, in a "most reasonably likely worst case
scenario", significantly limit its ability to provide its services for a period
of time, especially if such failure occurs in conjunction with third party or
infrastructure failures.
 
    Similarly, the Company could be significantly affected by the failure of one
or more significant suppliers, customers or components of the infrastructure, to
conduct their respective activities after 1999. Adverse effects on the Company
could include, among other things, business disruption, increased costs, and
loss of business.
 
FORWARD-LOOKING STATEMENTS
 
    This Report contains "forward-looking statements" within the meaning of the
U.S. Private Securities Litigation Reform Act of 1995. These forward-looking
statements include, but are not limited to, statements in the subsections of
"Management's Discussion and Analysis of Financial Condition and Results of
Operations" entitled "Overview", "North Sea", "Asia Pacific", "Gulf of Mexico",
"Liquidity and Capital Resources", "Euro", "The Year 2000 Issue", "Subsequent
Events", "Market Risk Discussion" and "Impact of New Accounting Standards". In
addition, this Report contains forward-looking statements relating to the
Company's performance in the "Description of Business" section. Actual and
future results and trends could differ materially from those set forth in such
statements due to various factors. Such factors include, among others: general
economic and business conditions; industry capacity; industry trends;
competition; currency fluctuations; the loss of any significant customers;
changes in business strategy or development plans; project performance;
availability and reliability of ships and other assets; availability, terms, and
deployment of capital; the ability of the Company and its significant customers
and suppliers to successfully implement timely Year 2000 solutions; availability
of qualified personnel; changes in, or failure or inability to comply with,
governmental regulations; adverse weather conditions; and other factors
referenced in this Report.
 
FACTORS AFFECTING REVENUES AND COSTS
 
    INDUSTRY CONDITIONS
 
    Demand for the Company's subsea services depends upon the condition of the
oil and gas industry and particularly upon capital expenditure budgets of the
companies engaged in the exploration, development and production of offshore oil
and gas. The prices of oil and gas and their uncertainty in the future, along
with forecasted growth in world oil and gas demand, will strongly influence the
extent of offshore exploration and development activities. Offshore oil and gas
field capital expenditures also are influenced by the sale and expiration dates
of offshore leases, the discovery rate of new oil and gas reserves in offshore
areas, local and international political and economic conditions and the ability
of oil and gas companies to access or generate capital. These factors are beyond
the control of SCS.
 
    OPERATING RISKS
 
    Subsea services involves operational risk and is increasingly dependent on
large, expensive, special-purpose ships and equipment. Hazards, such as ships
capsizing, sinking, grounding, colliding and sustaining damage from severe
weather conditions are inherent in the marine operations of subsea services.
These hazards can cause personal injury and loss of life, severe damage to, and
destruction of, property and equipment, pollution or environmental damage and
suspension of operations. All employees engaged in SCS's offshore operations are
covered by provisions of local and maritime laws, which generally provide
 
                                       16
<PAGE>
that employees or their representatives can bring actions against SCS for
damages for job-related injuries. In addition, although SCS generally seeks to
obtain indemnity agreements whenever possible from its customers requiring such
customers to hold SCS harmless in the event of structural damage, loss of
production or liability for pollution that originates below the water surface,
when obtained such contractual indemnification does not generally cover
liability resulting from the gross negligence or wilful misconduct of or
violation of law by employees or subcontractors of SCS and may not in all cases
be supported by adequate insurance maintained by the customer.
 
    CONTRACT BIDDING RISKS
 
    Reflecting market practice, a significant proportion of SCS's business is
performed on a fixed-price or turnkey basis. Gross profits realized on such
contracts vary, sometimes substantially, from the estimated amounts because of
changes in offshore job conditions, the risks inherent in marine construction
and variations in labor and equipment productivity from those originally
projected, and significant losses can result from performing fixed-price or
turnkey contracts. Under such contracts, SCS also typically bears a proportion
of the risk of delays and extra costs caused by adverse weather conditions or
other circumstances.
 
    On some projects the Company may be performing work under joint venture
agreements where the Company and its partner are jointly and severally liable
towards the customer for the performance of the contract while they between
themselves carry the full responsibility only for their own share of the work.
If the Company's joint venture partner in such arrangement fails to fulfill its
obligations, the Company could have to carry the resultant liability towards the
customer.
 
    PERCENTAGE-OF-COMPLETION PROJECT ACCOUNTING
 
    As most of SCS's contract revenue is recognized on a
percentage-of-completion basis, based on the ratio of costs incurred to the
total estimated costs at completion, contract revenues and gross profits for a
project may be adjusted in subsequent reporting periods from those originally
reported in prior periods. To the extent that these adjustments result in a
reduction or elimination of previously reported profits, SCS would recognize a
charge against current earnings that may be significant depending on the size of
the project or the adjustment.
 
    POLITICAL AND ECONOMIC RISK
 
    SCS's operations are geographically spread throughout the world, and are
therefore subject to various political, economic and other uncertainties,
including, among others, political instability, civil unrest, the risks of war,
asset seizure, nationalization of assets, renegotiation or nullification of
existing contracts, taxation policies, foreign exchange restrictions or
fluctuations and changing political conditions. Additionally, the ability of SCS
to compete in international markets may be adversely affected by governmental
regulations that favor or require the awarding of contracts to local
contractors, or by regulations requiring foreign contractors to employ citizens
of, or purchase supplies from, a particular jurisdiction. Furthermore, SCS's
subsidiaries may face governmentally imposed restrictions from time to time on
their ability to transfer funds to the Company. No predictions can be made as to
what governmental regulations applicable to SCS's operations may be enacted in
the future.
 
    SEASONALITY
 
    Over the past three years, approximately two-thirds of the Company's revenue
has been generated from work performed in the North Sea. In the future there is
likely to be increased activity in the Gulf of Mexico. Although it is less
apparent than in the past due to advances in technology, adverse weather
conditions in the North Sea and the Gulf of Mexico generally result in less
activity in these regions during
 
                                       17
<PAGE>
the winter months. Therefore, full year results are not likely to be a direct
multiple of any particular quarter or combination of quarters.
 
    DEPENDENCE ON SIGNIFICANT CUSTOMERS
 
    SCS's major customers are oil companies and large offshore contractors.
During 1998, one of SCS's customers accounted for more than 22%, and SCS's top
seven customers accounted for approximately 60%, of SCS's net operating revenue.
The loss of any one or more of these significant customers could have a material
adverse effect on SCS.
 
    COMPETITION
 
    The subsea business is highly competitive, and offshore subsea contractors
compete intensely for available projects. Contracts for SCS's services are
generally awarded on a competitive bid basis, and although customers may
consider, among other things, the availability and capability of equipment, and
the reputation and experience of the contractor, price is a primary factor in
determining which contractor is awarded a contract. Several of SCS's competitors
and potential competitors are larger and have greater financial and other
resources than SCS. In addition, increased activity levels may attract
additional competitors or equipment to the market and inhibit pricing
improvement.
 
    HAZARDOUS ACTIVITIES
 
    The operation of any ocean-going ship carries an inherent risk of
catastrophic marine disasters and property losses caused by adverse weather
conditions, mechanical failures, human error, war, terrorism, piracy, labor
stoppages and other circumstances or events. Any such event may result in loss
of revenues or increased costs.
 
    The Company carries insurance to protect against most of the
accident-related risks involved in the conduct of its business and it maintains
environmental damage and pollution insurance coverage. There can be no
assurance, however, that all risks are adequately insured against, that any
particular claim will be paid or that the Company will be able to procure
adequate insurance coverage at commercially reasonable rates in the future. In
particular, more stringent environmental regulations may result in increased
costs for, or the lack of availability of, insurance against the risks of
environmental damage or pollution.
 
    While the Company currently insures its ships against property loss due to a
catastrophic marine disaster, mechanical failure or collision, the loss of any
ship as a result of such an event could result in a substantial loss of
revenues, increased costs and other liabilities in excess of available insurance
and could have a material adverse effect on operating performance. Litigation
arising from such an occurrence may result in the Company being named as a
defendant in lawsuits asserting large claims.
 
    REGULATORY AND ENVIRONMENTAL MATTERS
 
    The Company operates in a number of different jurisdictions and is subject
to and affected by various types of governmental regulation, including national
laws and regulations and international conventions relating to ship safety and
design requirements, disposal of hazardous materials, discharge of oil or
hazardous substances, protection of the environment, food safety, and various
import and export requirements. These laws and regulations are becoming
increasingly complex, stringent and expensive to comply with, and there can be
no assurance that continued compliance with existing or future laws or
regulations will not adversely affect the operations of the Company. Significant
fines and penalties may be imposed for non-compliance.
 
    In addition, the Company could be held liable for remediation of, and
damages arising from, pollution caused by its ships and for releases of oil and
hazardous substances and debris from offshore production platforms, pipelines,
subsea facilities and other assets owned or operated by its customers, and for
releases
 
                                       18
<PAGE>
resulting from activities of, or equipment owned by, its subcontractors.
Although the Company generally negotiates contractual provisions requiring
customers to indemnify the Company in the event any such liability is imposed,
the Company has not obtained such indemnification in all cases. Moreover, such
indemnification does not generally cover liability resulting from the gross
negligence or wilful misconduct of, or violation of law by, employees or
subcontractors of the Company.
 
    CERTAIN FINANCIAL REQUIREMENTS
 
    The Company is party to material bank credit and other financing agreements
which impose certain financial requirements such as limitations on debt and the
types of businesses the Company may engage in. At the end of 1998, the Company
was in compliance with all of these credit/financing agreements. Except for
these financial requirements, none of these agreements imposes material
restrictions on the ability of the Company to incur additional indebtedness or
operate its businesses. Although management believes that current operating
plans will not be restricted by these requirements in the future, changes in
economic or business conditions, results of operations or other factors may in
the future result in circumstances in which the requirements restrict the
Company's plans or business operations
 
    LEVERAGE
 
    The degree to which the Company is leveraged may affect its ability to
obtain additional financing in the future for working capital, capital
expenditures, product and service development, and general corporate purposes,
to utilize cash flow from operations for purposes other than debt service, and
to overcome seasonal or other cyclical variations in its business. The ability
of the Company to satisfy its obligations and to reduce its debt is dependent on
the future performance of the Company, which will be subject to the prevailing
economic conditions and to financial, business, and other factors including
those beyond the Company's control.
 
    INTEREST RATES
 
    Approximately 40% of the Company's long-term indebtedness at March 31, 1999
is accrued at rates that fluctuate with the prevailing interest rates and,
accordingly, increases in such rates may increase the Company's interest cost.
 
    CAPITAL REQUIREMENTS
 
    The acquisition of new assets and properties, both for growth as well as
replacement, is capital intensive. The availability of new capital to finance
these expenditures depends on the prevailing market conditions and the
acceptability of financing terms offered to the Company. Management believes
that capital expected to be available under the various lines of credit,
financing agreements, and other sources and from disposition of existing assets
and properties as well as cash generated from operations, should be sufficient
to meet its capital requirements for the foreseeable future. No assurance,
however, can be given that financing will continue to be available on attractive
terms.
 
    FOREIGN CURRENCY FLUCTUATIONS
 
    Substantial portions of the Company's revenue and expenses are denominated
in currencies other than U.S. dollars. Fluctuations in these currencies can have
a significant impact on the Company's financial results. The Company engages in
hedging programs intended to reduce part of the Company's short-term exposure to
currency fluctuations. However, there can be no assurances that such efforts
will be successful. Hedging is limited to known and foreseeable exposures that
develop through normal business operations and to long-term business
investments. The Company does not attempt to hedge foreign earnings that are
translated into dollars for reporting purposes. Foreign currency fluctuations
have had and will continue to have an impact on reported financial results.
 
                                       19
<PAGE>
    TAXES
 
    The Company's operations are conducted in Norway and the U.K. as well as
certain other countries in Europe, Africa, the Middle East, Asia Pacific, North
America and South America. Net income earned from operations in most of such
countries are subject to corporate income taxes and withholding taxes on
dividends paid to other members of the Company's group.
 
    Certain of the Company's subsidiaries may be subject to income tax in the
U.S. and other jurisdictions. The subsidiaries which are incorporated in the
U.S. file a consolidated Federal income tax return, and other subsidiaries file
separate tax returns if and as required.
 
    RESTRUCTURING
 
    To operate in a price competitive manner, the Company regularly reviews its
operations. This review process may result in the closure of offices or
departments, the sale of assets or business lines, the termination of personnel,
or the reassessment of the useful life of assets or technology. Such actions may
affect the Company's results.
 
    LABOR RELATIONS
 
    The Company considers its relations with its employees and their unions to
be good and has not experienced any significant work stoppages. There can be no
assurances however that disruption of the Company's services or production, or
that larger labor disputes involving the industries the Company operates in will
not adversely affect the Company's results.
 
    ACQUISITION AND EXPANSION STRATEGY
 
    One element of the Company's strategy is to continue to grow through
selected acquisitions that further consolidate the markets in which the Company
operates. Likewise the Company plans on expanding its operations at existing or
new locations. There can be no assurance that any currently planned acquisitions
or expansions will be completed or that any currently planned or any additional
acquisitions or expansions will be successful in enhancing the operations or
profitability of the Company; that the Company will be able to identify suitable
additional acquisition candidates or areas for expansion; that it will have the
financial ability to consummate additional acquisitions or expansions; or that
it will be able to consummate such additional acquisitions or expansions on
terms favorable to the Company.
 
ITEM 9A. QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK
 
    The Company is exposed to market risk, including changes in interest rates
and currency exchange rates. To manage the volatility relating to these
exposures on a consolidated basis, the Company nets the exposure and takes
advantage of natural offsets and enters into derivative transactions for the
remaining currency exposures in accordance with the Company's policies. The
financial impact of these instruments are offset by corresponding changes in the
underlying exposure being hedged. The Company does not hold or issue derivative
instruments for trading purposes.
 
    The primary purpose of the Company's foreign currency hedging activities is
to protect against the volatility associated with foreign currency liabilities
or receipts created in the normal course of business. The Company's policy
prescribes the range of allowable hedging activity. The Company primarily
utilizes forward exchange contracts and purchased options with a duration of
generally less than twelve months.
 
    The Company uses a value-at-risk ("VAR") model to assess the market risk of
its derivative financial instruments. The model utilizes a variance/covariance
modeling technique. VAR models are intended to measure the maximum potential
loss for an instrument or portfolio assuming adverse changes in market
conditions, for a specific time period and confidence level. The Company's
estimated maximum potential one day loss in fair value of foreign exchange rate
instruments, calculated using the VAR model given a
 
                                       20
<PAGE>
95% confidence level, would not materially affect the consolidated financial
position, results of operations, or cash flow. Actual results in the future may
differ materially from these projected results due to actual developments in the
global financial markets.
 
    Based on the Company's overall interest rate exposures as of March 31, 1999,
a near-term change in interest rates would not materially affect the
consolidated financial position, results of operations, or cash flows.
 
    All of the Company's derivative activities are over the counter instruments
entered into with major financial credit institutions to hedge the Company's
committed exposures. All of the Company's derivative instruments are straight
forward foreign exchange forward contracts which subject the Company to a
minimum level of exposure risk. The Company does not consider it has a material
exposure to credit risk from third parties failing to perform according to the
terms of hedge instruments.
 
ITEM 10. DIRECTORS AND OFFICERS OF REGISTRANT
 
    SCS is a Luxembourg holding company and does not have officers as such. The
following is a list of the Directors of the Company and persons employed by its
subsidiaries who perform the indicated executive and administrative functions
for the combined business of the Company's subsidiaries:
 
<TABLE>
<CAPTION>
NAME                                           AGE*                              POSITION
------------------------------------------     -----     --------------------------------------------------------
<S>                                         <C>          <C>
Jacob Stolt-Nielsen.......................          67   Chairman of the Board of Directors
Christopher J. Wright.....................          64   Deputy Chairman of the Board of Directors
Alan Brunnen..............................          37   Chief Operating Officer and Vice President, U.K.
Andre Bursaux.............................          47   Vice President, SEAME
Brian Butler..............................          49   Vice President, Asia Pacific
Paul Frikstad.............................          48   Chief Financial Officer
John P. Laborde...........................          74   Director
Phillippe Lamoure.........................          46   Vice President, South America
Bjorn Myklatun............................          51   Vice President, Norway
Kevin Peterson............................          41   Vice President, North and Central America
Fernand Poimboeuf.........................          66   Director
Malcolm Seeley............................          47   Vice President, Engineering
J. Frithjof Skouveroe.....................          55   Director
Julian Thomson............................          50   Group Manager, Marketing and Communications
Stephen Vorley............................          44   Vice President, Field Development
Bernard Vossier...........................          54   Chief Executive Officer
Tom Welsh.................................          41   Vice President, Operations
Alan West.................................          40   Vice President, Subsea Construction
Mark Woolveridge..........................          64   Director
</TABLE>
 
------------------------
 
*   As of March 31, 1999.
 
    Under the terms of the Company's Articles of Incorporation, its Directors
may be elected for terms of up to six years and serve until their successors are
elected. It has been the Company's practice to elect directors for one year
terms. Under the Articles, the Board consists of not fewer than three Directors.
As of March 31, 1999, the Company's Board of Directors consisted of six members.
 
    Mr. Stolt-Nielsen has served as Chairman of the Board since 1993. Mr.
Stolt-Nielsen also serves as Chairman and Chief Executive Officer of SNSA. He
founded Seaway in 1973. Mr. Stolt-Nielsen is a Norwegian citizen.
 
    Mr. Wright has served as Deputy Chairman of the Board since 1993. He has
served as President and Chief Operating Officer of SNSA since 1986. Mr. Wright
was employed by British Petroleum plc ("BP")
 
                                       21
<PAGE>
from 1958 until the time he joined SNSA. Mr. Wright held a variety of positions
at BP including Senior Vice President of BP North America from 1982 to 1986. He
is a British citizen.
 
    Mr. Brunnen was appointed Chief Operating Officer on February 15, 1999. He
joined Seaway in 1992 and was involved in managing several major projects prior
to his appointment as Vice President, U.K. in 1995, a role which he continues to
fulfill. Prior to his appointment as Chief Operating Officer, he held the
position of Vice President, Organization and Process Development from February
15, 1998.
 
    Mr. Bursaux rejoined the Company in 1995 and was appointed Vice President,
SEAME, as of April 3, 1995. He came from a consulting firm specializing in
strategic marketing and management of company mergers. When previously with
Comex between the years of 1971-1985, he held various positions in engineering
and commercial activities, ultimately as Vice President, North Sea.
 
    Mr. Butler joined the Company as Vice President, Asia Pacific, as of
September 15, 1995. He was previously Managing Director of Swire Pacific
Offshore in Singapore and had held various technical and management positions in
the Swire Group involved with the oil and gas industry in the Middle East and
Far East.
 
    Mr. Frikstad joined the Company as Chief Financial Officer in June 1995. He
was previously Vice President, Offshore, in Mosvold Shipping A.S. and has more
than twenty years of experience in the offshore industry working for oil
companies and oil service contractors.
 
    Mr. Laborde has been a Director since 1993. He retired in 1995 as Chairman
of the Board, President and Chief Executive Officer of Tidewater Inc. and
continues to serve as a member of the Board of Directors of Tidewater. He is now
Chief Executive Officer of Laborde Marine Lifts, Inc. and also serves on the
boards of Stone Energy Corporation and Stewart Enterprises as well as the
Council of the American Bureau of Shipping. Mr. Laborde is a U.S. citizen.
 
    Mr. Lamoure was appointed Vice President, South America, as of March 1,
1995. He has been employed by the Company since 1974 when he joined Comex, most
recently General Manager for the Company's operations in France, Africa and
South America from 1994 to March 1995 and Operations Manager in Brazil from 1981
to 1994.
 
    Mr. Myklatun joined the company as Vice President, Norway as of September 7,
1998. Prior to joining the Company, he held the position of Managing Director of
Groner A.S. and has more than 23 years engineering experience in the North Sea.
 
    Mr. Peterson was appointed Vice President, North and Central America on
August 18, 1998, upon the acquisition of Ceanic Corporation. He has held various
senior management positions in the offshore industry over the last 25 years.
 
    Mr. Poimboeuf was appointed as a Director to the Company on April 16, 1998.
He has had a career of 33 years with Elf Aquitaine which included periods as
Deputy General Manager in Gabon, Executive Vice President of Texasgulf Inc. in
Houston and General Manager in Angola. Mr. Poimboeuf is a French citizen.
 
    Mr. Seeley was appointed Vice President, Engineering, as of September 27,
1996. He joined Comex in 1976 and was initially involved in engineering and
design engineering projects prior to being appointed manager for a number of
major subsea construction and development projects.
 
    Mr. Skouveroe has been a Director since 1993. He was Chairman of the Board
and Chief Executive Officer of Seaway from 1990 until it was acquired by SNSA in
1992. From 1985 to 1990, he was President and Second Vice Chairman of Seaway.
From 1982 until 1985, Mr. Skouveroe served as President of Stolt-Nielsen Seaway
Contracting A/S, a predecessor of Seaway. Mr. Skouveroe is a Norwegian citizen.
 
    Mr. Thomson first joined Seaway in September 1990 as Business Development
Manager. He rejoined the Company in November 1995 as Group Manager, Marketing
and Communications. A former Royal Navy officer, he has 20 years of experience,
most of which have been in the offshore and subsea industry.
 
                                       22
<PAGE>
    Mr. Vorley was appointed Vice President, Field Development, as of July 17,
1995. He joined Comex in 1983 and prior to 1995 worked in engineering, project
and commercial posts in the U.K. and Norway.
 
    Mr. Vossier was appointed Chief Executive Officer of the Company as of May
23, 1995. He previously served as Chief Operating Officer of the Company from
December 1994 to May 1995. He joined Comex in 1974 and has held numerous
management positions in operations and marketing.
 
    Mr. Welsh was appointed Vice President, Operations, as of December 1, 1998.
He first worked for Comex from 1985 to 1988. After working as a consultant for a
number of years he rejoined the Company in 1992 and worked in engineering and
project management roles on a number of important projects as well as Vice
President, Flowline Lay, prior to his current position.
 
    Mr. West was appointed Vice President, Subsea Construction, as of July 17,
1995. He joined Comex in 1982 and has worked in engineering and the management
of major projects in the North Sea and other parts of the world.
 
    Mr. Woolveridge has been a Director since 1993. He held a number of
positions with BP since 1968 and most recently served as Chief Executive of BP
Engineering from 1989 until his retirement in 1992. He also was General Manager,
Oil and Gas Developments, responsible for field development projects in the U.K.
and Norwegian sectors of the North Sea, and served on the board of BP Oil Ltd.
Mr. Woolveridge is a British citizen.
 
    CHANGES SINCE MARCH 31, 1999
 
    Mr. Niels Gregers Stolt-Nielsen was elected as a Director on April 15, 1999.
Mr. Stolt-Nielsen has also served as Managing Director of Stolt Sea Farm since
June 1996. He previously worked in Stolt-Nielsen's transportation group. He is a
Norwegian Citizen.
 
    Mr. Niels Gregers Stolt-Nielsen is the son of Mr. Jacob Stolt-Nielsen.
 
ITEM 11. COMPENSATION OF DIRECTORS AND OFFICERS
 
    As described above, SCS does not have officers, but certain persons employed
by its subsidiaries perform executive and administrative functions for the
combined business of the Company's subsidiaries. The aggregate annual
compensation paid to the 13 officers performing such executive functions for
SCS, as a group, for the fiscal year ended November 30, 1998 (including certain
benefits) was $2,426,000. In addition, $178,000 was contributed on behalf of
such officers to defined contribution pension plans. During 1998, Directors of
Stolt Comex Seaway S.A. who were affiliated with the Company or a subsidiary of
SNSA received no compensation for their services, as such, but received
reimbursement of their out-of-pocket expenses. All non-executive directors of
the Company received an annual fee of $20,000, plus expenses in 1998.
 
PROFIT SHARING PLAN
 
    SCS has a Profit Sharing Plan which pays 10% of the Company's net profit
(after specified adjustments) to its officers and employees worldwide other than
those covered by collective bargaining agreements. The determination of an
employee's individual award is based on performance, salary and overall
contribution to the Company. The Profit Sharing Plan is administered by a
Compensation Committee appointed by the SCS Board of Directors. For the fiscal
year ended November 30, 1998, a total provision of $5,700,000 has been made for
payment under the Profit Sharing Plan. The payment of Profit Sharing for 1998
will not be made until July 1999 and the portion to be allocated to officers has
not yet been determined.
 
                                       23
<PAGE>
ITEM 12. OPTIONS TO PURCHASE SECURITIES FROM REGISTRANT OR SUBSIDIARIES
 
    The Company has a Stock Option Plan (the "Plan") covering 3.3 million Common
Shares and 1.6 million Class A Shares. Options may be granted under the Plan
exercisable for periods of up to ten years. The options granted under the Plan
will be at an exercise price not less than the fair market value per share at
the time the option is granted. The Plan is administered by a Compensation
Committee appointed by the SCS Board of Directors. The Compensation Committee
awards options based on the grantee's position in the Company, degree of
responsibility, seniority, contribution to the Company and such other factors as
it deems relevant under the circumstances.
 
    As of April 30, 1999, a total of 1,137,400 options exercisable for Common
Shares and 340,965 options exercisable for Class A Shares had been granted to
the Company's subsidiaries' employees, of which 615,555 Common and 314,465 Class
A Shares remain outstanding and 264,880 Common and 137,316 Class A Shares are
currently exercisable. Of the total remaining outstanding, options for 467,254
Common Shares and 143,812 Class A Shares have been granted to employees who are
Directors and executive officers of SCS. The outstanding options are exercisable
at the respective prices set forth below and expire on the dates indicated:
 
<TABLE>
<CAPTION>
                                                                        OPTIONS
                                                           OPTIONS     CURRENTLY     EXERCISE
AWARD YEAR                                               OUTSTANDING  EXERCISABLE      PRICE      EXPIRATION DATE
-------------------------------------------------------  -----------  -----------  -------------  ---------------
<S>                                                      <C>          <C>          <C>            <C>
COMMON SHARES
1993...................................................      11,580       11,580    $    5.1667         May 2003
1994...................................................      27,875       27,875         3.0000         Apr 2004
1995...................................................      87,000       65,250         2.7917         Jun 2005
1996...................................................      96,500       72,375         2.7083         Mar 2006
1997...................................................     175,600       87,800         5.7917         Mar 2007
1998...................................................     217,000           --        16.5830         Jun 2008
                                                         -----------  -----------
  Total................................................     615,555      264,880
                                                         -----------  -----------
                                                         -----------  -----------
 
CLASS A SHARES
1993...................................................       5,790        5,790    $    5.1667         May 2003
1994...................................................      13,375       13,375         3.0000         Apr 2004
1995...................................................      47,750       35,813         2.7917         Jun 2005
1996...................................................      51,250       38,438         2.7083         Mar 2006
1997...................................................      87,800       43,900         5.7917         Mar 2007
1998...................................................     108,500           --        16.5830         Jun 2008
                                                         -----------  -----------
  Total................................................     314,465      137,316
                                                         -----------  -----------
                                                         -----------  -----------
</TABLE>
 
    As part of the acquisition of the former Ceanic Corporation, holders of
Ceanic shares were entitled to exercise all vested and one-third of their
unvested Ceanic options, or to convert any portion thereof to vested SCS Common
Shares. Their remaining two-thirds unvested Ceanic shares were automatically
converted to unvested SCS Common Shares at the date of acquisition. As of April
30, 1999, a total of 1,018,908 options exercisable for Common Shares and nil
options exercisable for Class A Shares had been granted to the Company's
subsidiaries' employees. Options outstanding and options currently exercisable
 
                                       24
<PAGE>
as of April 30, 1999 include 953,201 Common and nil Class A Shares and 139,179
Common and nil Class A Shares, respectively. The following table reflects this:
 
<TABLE>
<CAPTION>
                                                                        OPTIONS
                                                           OPTIONS     CURRENTLY     EXERCISE
AWARD YEAR                                               OUTSTANDING  EXERCISABLE      PRICE      EXPIRATION DATE
-------------------------------------------------------  -----------  -----------  -------------  ---------------
<S>                                                      <C>          <C>          <C>            <C>
COMMON SHARES
1994...................................................       3,838        3,838    $    5.2100         Jul 2004
1996...................................................       5,758        5,758         5.8200         Apr 2006
1997...................................................     197,665           --         6.2500         Apr 2007
1997...................................................      15,353           --         7.4700         Jun 2007
1997...................................................       7,676        7,676         7.8200         Jun 2007
1997...................................................     500,294       85,443        10.8100         Sep 2007
1997...................................................       9,596           --         8.3800         Dec 2007
1998...................................................       7,196        2,399         7.8200         Jul 2008
1998...................................................       7,677           --         6.7700         Feb 2008
1998...................................................       3,839           --         7.1200         Feb 2008
1998...................................................       3,839           --         6.7000         Feb 2008
1998...................................................      19,190           --         7.3800         Feb 2008
1998...................................................       1,919           --         8.7300         Mar 2008
1998...................................................       8,636        2,879         8.4200         Mar 2008
1998...................................................       7,676           --        10.2900         Mar 2008
1998...................................................      17,274        9,596        10.2500         Apr 2008
1998...................................................      14,393        4,797        11.2000         May 2008
1998...................................................      52,294        5,278        10.7700         Mar 2008
1998...................................................      47,977           --        11.0300         May 2008
1998...................................................       5,757           --        10.9900         May 2008
1998...................................................       5,758        1,919        10.3300         May 2008
1998...................................................       9,596        9,596         7.3800         Nov 2008
                                                         -----------  -----------
Total                                                       953,201      139,179
                                                         -----------  -----------
                                                         -----------  -----------
</TABLE>
 
ITEM 13. INTEREST OF MANAGEMENT IN CERTAIN TRANSACTIONS
 
    The discussion of related party transactions appearing as Note 14 to
Consolidated Financial Statements, which is part of Item 18 of this Report, is
incorporated herein by reference.
 
                                       25
<PAGE>
                                    PART III
 
ITEM 15. DEFAULTS UPON SENIOR SECURITIES
 
    None.
 
ITEM 16. CHANGES IN SECURITIES, CHANGES IN SECURITY FOR REGISTERED SECURITIES
  AND USE OF PROCEEDS
 
    None.
 
                                    PART IV
 
ITEM 17. FINANCIAL STATEMENTS
 
    The Company has elected to provide financial statements for the fiscal year
ended November 30, 1998 and the related information pursuant to Item 18.
 
ITEM 18. FINANCIAL STATEMENTS
 
    1. Consolidated Financial Statements of Stolt Comex Seaway S.A. and
Subsidiaries
 
       Report of Independent Public Accountants.
 
       Consolidated Balance Sheets as of November 30, 1998 and 1997.
 
       Consolidated Statements of Income for the years ended November 30, 1998,
       1997 and 1996.
 
       Consolidated Statements of Shareholders' Equity for the years ended
       November 30, 1998, 1997, and 1996.
 
       Consolidated Statements of Cash Flows for the years ended November 30,
       1998, 1997 and 1996.
 
       Notes to Consolidated Financial Statements.
 
    The consolidated financial statements and related notes referred to above
and the report of Arthur Andersen, the Company's independent public accountants,
appearing on pages 26 through 45 of the Company's 1998 Annual Report filed with
the Securities and Exchange Commission on Form 6-K are incorporated herein by
reference.
 
    2. Report of Independent Public Accountants on Schedules
 
       Supplementary Schedules
 
       Schedule II Valuation and Qualifying Accounts
 
ITEM 19. FINANCIAL STATEMENTS AND EXHIBITS
 
    (a) Financial Statements.
 
       See list in Item 18.
 
    (b) Exhibits.
 
<TABLE>
<C>          <S>
       2.1   Consent of Arthur Andersen, Independent Public Accountants.
       2.2   Consent of Elvinger, Hoss & Prussen.
       2.3   Amended Articles of Incorporation.
       2.4   Company's 1998 Annual Report, pages 17 through 45.
       2.5   Revolving Credit Facility, dated as of December 19, 1997, among Stolt Comex
             Seaway S.A., Midland Bank plc, Den norske Bank ASA and the Banks listed
             therein.
       2.6   Loan Facility Agreement, dated April 1, 1999, among Adviesburo Energietechniek
             Van De Pol B.V., Stolt Comex Seaway S.A., Den norske Bank ASA, Bank of America
             National Trust and Savings Association and the Banks listed therein.
        27   Financial Data Schedule.
</TABLE>
 
                                       26
<PAGE>
                                   SIGNATURES
 
    Pursuant to the requirements of Section 12 of the Securities Exchange Act of
1934, the Registrant certifies that it meets all of the requirements for filing
on Form 20-F and has duly caused this annual report to be signed on its behalf
by the undersigned, thereunto duly authorized.
 
<TABLE>
<S>                             <C>  <C>
                                STOLT COMEX SEAWAY S.A.
 
                                By:  /s/ CHRISTOPHER J. WRIGHT
                                     -----------------------------------------
                                     Name: Christopher J. Wright
                                     Title: Deputy Chairman of the Board of
                                            Directors
 
                                By:  /s/ PAUL FRIKSTAD
                                     -----------------------------------------
                                     Name: Paul Frikstad
                                     Title: Chief Financial Officer
</TABLE>
 
Date: May 12, 1999
 
                                       27
<PAGE>
               INDEX TO REPORT OF INDEPENDENT PUBLIC ACCOUNTANTS
                          AND SUPPLEMENTARY SCHEDULES
 
<TABLE>
<CAPTION>
                                                                                                                PAGE
                                                                                                                -----
<S>                                                                                                          <C>
Report of Independent Public Accountants...................................................................         F-2
Supplementary Schedules
  Schedule II--Valuation and Qualifying Accounts...........................................................         F-3
</TABLE>
 
                                      F-1
<PAGE>
                    REPORT OF INDEPENDENT PUBLIC ACCOUNTANTS
 
TO STOLT COMEX SEAWAY S.A.:
 
    We have audited in accordance with generally accepted auditing standards in
the United States, the consolidated financial statements included in Stolt Comex
Seaway S.A.'s Annual Report to Shareholders incorporated by reference in this
Form 20-F, and have issued our report thereon dated February 24, 1999. Our
audits were made for the purpose of forming an opinion on those statements taken
as a whole. The schedules listed in the Index on page F-1 are the responsibility
of the Company's management and are presented for purposes of complying with the
Securities and Exchange Commission's rules and are not part of the basic
consolidated financial statements. These schedules have been subjected to the
auditing procedures applied in the audits of the basic consolidated financial
statements and, in our opinion, fairly state in all material respects the
financial data required to be set forth therein in relation to the basic
consolidated financial statements taken as a whole.
 
                                           ARTHUR ANDERSEN
 
Glasgow, Scotland
May 11, 1999
 
                                      F-2
<PAGE>
                                                                     SCHEDULE II
 
                    STOLT COMEX SEAWAY S.A. AND SUBSIDIARIES
 
                       VALUATION AND QUALIFYING ACCOUNTS
 
                             (AMOUNTS IN THOUSANDS)
 
<TABLE>
<CAPTION>
                                                 BALANCE AT    CHARGED TO    WRITE-OFFS
                                                BEGINNING OF    COSTS AND    AGAINST THE     OTHER ADD     BALANCE AT
                                                   PERIOD       EXPENSES       RESERVE     (DEDUCT) (A)   END OF PERIOD
                                                -------------  -----------  -------------  -------------  -------------
<S>                                             <C>            <C>          <C>            <C>            <C>
For the year ended November 30, 1996:
Allowance for doubtful accounts...............    $   1,449     $   1,123     $    (124)     $     (24)     $   2,424
                                                     ------    -----------        -----          -----         ------
                                                     ------    -----------        -----          -----         ------
For the year ended November 30, 1997:
Allowance for doubtful accounts...............    $   2,424     $     222     $    (137)     $    (300)     $   2,209
                                                     ------    -----------        -----          -----         ------
                                                     ------    -----------        -----          -----         ------
For the year ended November 30, 1998:
Allowance for doubtful accounts...............    $   2,209     $   2,766     $    (282)     $      12      $   4,750
                                                     ------    -----------        -----          -----         ------
                                                     ------    -----------        -----          -----         ------
</TABLE>
 
------------------------
 
(a) Includes the effect of exchange rate changes on beginning balances of
    valuation and qualifying accounts, except as otherwise noted.
 
                                      F-3