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                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                             ---------------------

                                  SCHEDULE TO
                                  (RULE 13e-4)
           TENDER OFFER STATEMENT UNDER SECTION 14(d)(1) OR 13(e)(1)
                     OF THE SECURITIES EXCHANGE ACT OF 1934
                             ---------------------

                               SIPEX CORPORATION
         (Name of Subject Company (Issuer) and Filing Person (Offeror))
                             ---------------------
          OPTIONS TO PURCHASE COMMON STOCK, PAR VALUE $0.01 PER SHARE
                         (Title of Class of Securities)
                             ---------------------
                                   829909100
         (CUSIP Number of Class of Securities' Underlying Common Stock)
                             ---------------------
                                 WALID MAGHRIBI
                     PRESIDENT AND CHIEF EXECUTIVE OFFICER
                               SIPEX CORPORATION
                            233 SOUTH HILLVIEW DRIVE
                               MILPITAS, CA 95035
                              TEL: (408) 934-7500
(Name, address and telephone number of person authorized to receive notices and
                   communications on behalf of filing person)
                             ---------------------
                                   COPIES TO:
                             JEFFREY D. SAPER, ESQ.
                               JACK HELFAND, ESQ.
                              JASON BORREVIK, ESQ.
                       WILSON SONSINI GOODRICH & ROSATI,
                            PROFESSIONAL CORPORATION
                               650 PAGE MILL ROAD
                        PALO ALTO, CALIFORNIA 94304-1050
                                 (650) 493-9300

                           CALCULATION OF FILING FEE



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               TRANSACTION VALUATION*                                 AMOUNT OF FILING FEE
-----------------------------------------------------------------------------------------------------------
                                                   
                     $2,386,813                                              $219.59
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* Calculated solely for purposes of determining the filing fee. This amount
  assumes that options to purchase 2,495,052 shares of common stock of SIPEX
  CORPORATION having an aggregate value of $2,386,813 as of October 9, 2002 will
  be exchanged or cancelled pursuant to this offer. The aggregate value of such
  options was calculated based on the Black-Scholes option pricing model. The
  amount of the filing fee, calculated in accordance with Rule 0-11(b) of the
  Securities Exchange Act of 1934, as amended, equals $92 for each $1,000,000 of
  the value of the transaction.

[ ] Check the box if any part of the fee is offset as provided by Rule
    0-11(a)(2) and identify the filing with which the offsetting fee was
    previously paid. Identify the previous filing by registration statement
    number, or the Form or Schedule and the date of its filing.

Amount Previously Paid:                                          Not applicable.
Form or Registration No.:                                        Not applicable.
Filing party:                                                    Not applicable.
Date filed:                                                      Not applicable.

[ ] Check the box if the filing relates solely to preliminary communications
    made before the commencement of a tender offer.

Check the appropriate boxes below to designate any transactions to which the
statement relates:
       [ ] third party tender offer subject to Rule 14d-1.
       [X] issuer tender offer subject to Rule 13e-4.
       [ ] going-private transaction subject to Rule 13e-3.
       [ ] amendment to Schedule 13D under Rule 13d-2.

Check the following box if the filing is a final amendment reporting the results
of the tender offer: [ ]

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     This Tender Offer Statement on Schedule TO relates to an offer by SIPEX
CORPORATION, a Massachusetts corporation ("SIPEX" or the "Company"), to exchange
(the "Exchange Offer") options to purchase an aggregate of 2,495,052 shares of
the Company's common stock, whether vested or unvested, that have been granted
under its 1996 Incentive Stock Option Plan, 1997 Stock Option Plan, 2000
Non-Qualified Stock Option Plan, 2002 Nonstatutory Stock Option Plan and certain
stand-alone Option Plans that have exercise prices greater than 7.50 per share
(the "Eligible Options") and that are held by eligible employees. These Eligible
Options may be exchanged for new options (the "New Options") that will be
granted under upon the terms and subject to the conditions set forth in: (i) the
Offer to Exchange, dated October 10, 2002 (the "Offer to Exchange"); (ii) the
related letter from Walid Maghribi dated October 10, 2002; (iii) the Election
Form; and (iv) the Withdrawal Form. These documents, as they may be amended or
supplemented from time to time, together constitute the "Disclosure Documents"
and are attached to this Schedule TO as Exhibits (a)(1)(a) through (a)(1)(d),
respectively. An "eligible employee" refers to all persons who are employees as
of October 10, 2002, and live and work in the United States and remain employees
through the date on which the New Options are granted. Members of the Company's
Board of Directors and the Company's executive officers are not "eligible
employees."

     The information in the Disclosure Documents, including all schedules and
annexes to the Disclosure Documents, is incorporated by reference in answer to
the items required in this Schedule TO.

ITEM 1. SUMMARY TERM SHEET.

     The information set forth under the caption "Summary Term Sheet" in the
Offer to Exchange is incorporated herein by reference.

ITEM 2. SUBJECT COMPANY INFORMATION.

     (a) NAME AND ADDRESS.

     SIPEX is the issuer of the securities subject to the Exchange Offer. The
address of the Company's principal executive office is 233 South Hillview Drive,
Milpitas, CA 95035 and the telephone number at that address is (408) 934-7500.
The information set forth in the Offer to Exchange under the caption "The
Offer -- Information concerning SIPEX" is incorporated herein by reference.

     (b) SECURITIES.

     The subject class of securities consists of the Eligible Options. The
actual number of shares of common stock subject to the New Options to be issued
in the Exchange Offer will depend on the number of shares of common stock
subject to the unexercised options tendered by eligible employees and accepted
for exchange and cancelled. The information set forth in the Offer to Exchange
under the captions "Summary Term Sheet," "Risks of Participating in the Offer,"
and the sections under the caption "The Offer" entitled "Number of options;
expiration date," "Acceptance of options for exchange and issuance of new
options," "Source and amount of consideration; terms of new options" is
incorporated herein by reference.

     (c) TRADING MARKET AND PRICE.

     The information set forth in the Offer to Exchange under the caption "The
Offer -- Price range of shares underlying the options" is incorporated herein by
reference.

ITEM 3. IDENTITY AND BACKGROUND OF FILING PERSON.

     (a) NAME AND ADDRESS.

     The filing person is the issuer. The information set forth under Item 2(a)
above is incorporated by reference.

     Pursuant to General Instruction C to Schedule TO, the information set forth
on Schedule A to the Offer to Exchange is incorporated herein by reference.

                                        2


ITEM 4. TERMS OF THE TRANSACTION.

     (a) MATERIAL TERMS.

     The information set forth in the Offer to Exchange under the captions
"Summary Term Sheet" and the sections under the caption "The Offer" entitled
"Eligibility," "Number of options; expiration date," "Procedures for electing to
exchange options," "Withdrawal rights and change of election," "Acceptance of
options for exchange and issuance of new options," "Conditions of the offer,"
"Source and amount of consideration; terms of new options," "Price range of
shares underlying the options," "Status of options acquired by us in the offer;
accounting consequences of the offer," "Legal matters; regulatory approvals,"
and "Material U.S. federal income tax consequences" and "Extension of offer;
termination; amendment" is incorporated herein by reference.

     (b) PURCHASES.

     The information set forth in the Offer to Exchange under the caption "The
Offer -- Interests of directors and officers; transactions and arrangements
concerning the options" is incorporated herein by reference.

ITEM 5. PAST CONTACTS, TRANSACTIONS, NEGOTIATIONS AND ARRANGEMENTS.

     (e)AGREEMENTS INVOLVING THE SUBJECT COMPANY'S SECURITIES.

     The information set forth in the Offer to Exchange under the caption "The
Offer -- Interests of directors and officers; transactions and arrangements
concerning the options" is incorporated by reference. The eligible option plans
and related option agreements attached hereto as Exhibits (d)(1) through (d)(10)
contain information regarding the subject securities.

ITEM 6. PURPOSES OF THE TRANSACTION AND PLANS OR PROPOSALS.

     (a) PURPOSES.

     The information set forth in the Offer to Exchange under the captions
"Summary Term Sheet" and "The Offer -- Purpose of the offer" is incorporated
herein by reference.

     (b) USE OF SECURITIES ACQUIRED.

     The information set forth in the Offer to Exchange under the captions "The
Offer -- Acceptance of options for exchange and issuance of new options" and
"The Offer -- Status of options acquired by us in the offer; accounting
consequences of the offer" is incorporated herein by reference.

     (c) PLANS.

     The information set forth in the Offer to Exchange under the captions "The
Offer -- Purpose of the offer" and the "The Offer -- Information concerning
SIPEX" incorporated herein by reference.

ITEM 7. SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION.

     (a) SOURCE OF FUNDS.

     The information set forth in the Offer to Exchange under the captions "The
Offer -- Source and amount of consideration; terms of new options" is
incorporated herein by reference.

     (b) CONDITIONS.

     Not applicable.

     (d) BORROWED FUNDS.

     Not applicable.

                                        3


ITEM 8. INTEREST IN SECURITIES OF THE SUBJECT COMPANY.

     (a) SECURITIES OWNERSHIP.

     The information set forth in the Offer to Exchange under the caption "The
Offer -- Interests of directors and officers; transactions and arrangements
concerning the options" is incorporated herein by reference.

     (b) SECURITIES TRANSACTIONS.

     The information set forth in the Offer to Exchange under the caption "The
Offer -- Interests of directors and officers; transactions and arrangements
concerning the options" is incorporated herein by reference.

ITEM 9. PERSON/ASSETS, RETAINED, EMPLOYED, COMPENSATED OR USED.

     (a) SOLICITATIONS OR RECOMMENDATIONS.

     Not applicable.

ITEM 10. FINANCIAL STATEMENTS.

     (a) FINANCIAL INFORMATION.

     The information set forth in Schedule B to the Offer to Exchange and in the
Offer to Exchange under the captions "The Offer -- Information concerning
SIPEX," "The Offer -- Financial statements," and "The Offer -- Additional
information." The Company's Annual Report on Form 10-K and the Quarterly Reports
on Form 10-Q can also be accessed electronically on the Securities and Exchange
Commission's website at http://www.sec.gov.

     (b) PRO FORMA INFORMATION.

     Not applicable.

ITEM 11. ADDITIONAL INFORMATION.

     (a) AGREEMENTS, REGULATORY REQUIREMENTS AND LEGAL PROCEEDINGS.

     The information set forth in the Offer to Exchange under the caption "The
Offer -- Legal matters; regulatory approvals" is incorporated herein by
reference.

     (b) OTHER MATERIAL INFORMATION.

     Not applicable.

ITEM 12. EXHIBITS.



 EXHIBIT
 NUMBER                             DESCRIPTION
---------                           -----------
         
(a)(1)(a)   Offer to Exchange Certain Outstanding Options for New
            Options dated October 10, 2002.
(a)(1)(b)   Letter from Walid Maghribi dated October 10, 2002.
(a)(1)(c)   Election Form.
(a)(1)(d)   Withdrawal Form.
(a)(1)(e)   Form of Promise to Grant Stock Option.
(b)         Not Applicable.
(d)(1)      1996 Incentive Stock Option Plan (filed as Exhibit 10.5 to
            the Company's registration statement on Form S-1 dated
            February 13, 1996, File No. 333-1328 and incorporated herein
            by reference).
   (2)      1997 Stock Option Plan (filed as Exhibit 4.4 to the
            Company's registration statement on Form S-8 dated July 29,
            1997, File No. 333-32329 and incorporated herein by
            reference).
   (3)      Amended 2000 Non-Qualified Stock Option Plan.


                                        4




 EXHIBIT
 NUMBER                             DESCRIPTION
---------                           -----------
         
   (4)      2002 Nonstatutory Stock Option Plan (filed as Exhibit 4.3 to
            the Company's Registration Statement on Form S-8 dated
            November 21, 2001, File No. 333-7380, and incorporated
            herein by reference).
   (5)      Form of stock option agreement for SIPEX 1996 Incentive
            Stock Option Plan (filed as Exhibit 10.5 to the Company's
            registration statement on Form S-1 dated February 13, 1996,
            File No. 333-1328 and incorporated herein by reference).
   (6)      Form of stock option agreement for SIPEX 1997 Stock Option
            Plan (filed as Exhibit 4.4 to the Company's registration
            statement on Form S-8 dated July 29, 1997, File No.
            333-32329 and incorporated herein by reference).
   (7)      Form of Non-Qualified Option Agreement dated August 12, 1999
            (filed as Exhibit 4.4 to the Company's registration
            statement on Form S-8 dated March 1, 2000, File No.
            333-31410 and incorporated herein by reference).
   (8)      Form of Non-Qualified Option Agreement dated November 23,
            1999 (filed as Exhibit 4.5 to the Company's registration
            statement on Form S-8 dated March 1, 2000, File No.
            333-31410 and incorporated herein by reference).
   (9)      Form of stock option agreement for SIPEX 2000 Non-Qualified
            Stock Option Plan (filed as Exhibit 4.4 to the Company's
            registration statement on Form S-8 dated May 24, 2001, File
            No. 333-61560 and incorporated herein by reference).
   (10)     Form of stock option agreement for SIPEX 2002 Nonstatutory
            Stock Option Plan (filed as Exhibit 4.4 to the Company's
            Registration Statement on Form S-8 dated November 21, 2001,
            File No. 333-7380, and incorporated herein by reference).
(g)         Not applicable.
(h)         Not applicable.


ITEM 13. INFORMATION REQUIRED BY SCHEDULE 13E-3.

     (a) Not applicable.

                                        5


                                   SIGNATURE

     After due inquiry and to the best of my knowledge and belief, I certify
that the information set forth in this Schedule TO is true, complete and
correct.

                                          SIPEX CORPORATION
                                          /s/  Walid Maghribi
                                          --------------------------------------
                                                      Walid Maghribi
                                          President and Chief Executive Officer

Date: October 10, 2002

                                        6


                               INDEX TO EXHIBITS



EXHIBIT
NUMBER                              DESCRIPTION
-------                             -----------
         
(a)(1)(a)   Offer to Exchange Certain Outstanding Options for New
            Options dated October 10, 2002.
(a)(1)(b)   Letter from Walid Maghribi dated October 10, 2002.
(a)(1)(c)   Election Form.
(a)(1)(d)   Withdrawal Form.
(a)(1)(e)   Form of Promise to Grant Stock Option.
(d)(1)      1996 Incentive Stock Option Plan (filed as Exhibit 10.5 to
            the Company's registration statement on Form S-1 dated
            February 13, 1996, File No. 333-1328 and incorporated herein
            by reference).
   (2)      1997 Stock Option Plan (filed as Exhibit 4.4 to the
            Company's registration statement on Form S-8 dated July 29,
            1997, File No. 333-32329 and incorporated herein by
            reference).
   (3)      Amended 2000 Non-Qualified Stock Option Plan.
   (4)      2002 Nonstatutory Stock Option Plan (filed as Exhibit 4.3 to
            the Company's Registration Statement on Form S-8 dated
            November 21, 2001, File No. 333-7380, and incorporated
            herein by reference).
   (5)      Form of stock option agreement for SIPEX 1996 Incentive
            Stock Option Plan (filed as Exhibit 10.5 to the Company's
            registration statement on Form S-1 dated February 13, 1996,
            File No. 333-1328 and incorporated herein by reference).
   (6)      Form of stock option agreement for SIPEX 1997 Stock Option
            Plan (filed as Exhibit 4.4 to the Company's registration
            statement on Form S-8 dated July 29, 1997, File No.
            333-32329 and incorporated herein by reference).
   (7)      Form of Non-Qualified Option Agreement dated August 12, 1999
            (filed as Exhibit 4.4 to the Company's registration
            statement on Form S-8 dated March 1, 2000, File No.
            333-31410 and incorporated herein by reference).
   (8)      Form of Non-Qualified Option Agreement dated November 23,
            1999 (filed as Exhibit 4.5 to the Company's registration
            statement on Form S-8 dated March 1, 2000, File No.
            333-31410 and incorporated herein by reference).
   (9)      Form of stock option agreement for SIPEX 2000 Non-Qualified
            Stock Option Plan (filed as Exhibit 4.4 to the Company's
            registration statement on Form S-8 dated May 24, 2001, File
            No. 333-61560 and incorporated herein by reference).
  (10)      Form of stock option agreement for SIPEX 2002 Nonstatutory
            Stock Option Plan (filed as Exhibit 4.4 to the Company's
            Registration Statement on Form S-8 dated November 21, 2001,
            File No. 333-7380, and incorporated herein by reference).