<PAGE>
                                                                     EXHIBIT 4.7
                                             MANDATORY REDEMPTION DATE EXTENSION

[LETTERHEAD OF SYSTEMONE]
--------------------------------------------------------------------------------
     SystemOne Technologies Inc. - 8305 NW 27th Street - Suite 107 - Miami,
                FL 33122 - Tel: 305-593-8015 - Fax: 305-593-8016

                                December 9, 2002

To the holders of Preferred Stock set forth on the signature page hereto:

                  RE:      MANDATORY REDEMPTION RIGHTS PURSUANT TO SECTION 10(b)
                  OF EACH OF THE CERTIFICATES OF DESIGNATION (THE "CERTIFICATES
                  OF DESIGNATIONS") OF THE SERIES B CONVERTIBLE PREFERRED STOCK,
                  SERIES C CONVERTIBLE PREFERRED STOCK AND SERIES D CONVERTIBLE
                  PREFERRED STOCK (COLLECTIVELY, THE "PREFERRED STOCK") OF
                  SYSTEMONE TECHNOLOGIES INC. (THE "COMPANY").

Ladies and Gentlemen:

         Pursuant to Section 10(b) of each of the Certificates of Designation,
the Company is obligated to redeem all of the outstanding shares of Preferred
Stock on May 17, 2004 (the "Mandatory Redemption Date"). Concurrently herewith,
the Company is exchanging its currently outstanding 8.25% Subordinated
Convertible Notes due February 23, 2003, for new 8.25% Subordinated Convertible
Notes (the "Notes") due December 31, 2005. Section 2(f) of the Notes prohibits
the Company from, without the consent of the holders of the Notes, redeeming any
of its outstanding equity securities while the Notes remain outstanding. If the
Preferred Stock is not redeemed on or prior to the Mandatory Redemption Date,
then pursuant to Section 10(d) of the Certificates of Designation, the
conversion price for the Preferred Stock would be reduced.

         Effective upon execution hereof, the undersigned holders of 100% of the
outstanding shares of the Preferred Stock (the "Holders") hereby agree that the
Mandatory Redemption Date shall be deemed to be the earlier to occur of (i) the
90th day after the date that all of the Notes shall have been repaid in full and
(ii) March 31, 2006, but in no event shall the Mandatory Redemption Date be
deemed to occur prior to May 17, 2004.

         Each of the Holders agrees further that such Holder shall not transfer
any shares of Preferred Stock unless the transferee acknowledges and agrees to
the terms hereof.

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<PAGE>
                                                                     EXHIBIT 4.7
                                             MANDATORY REDEMPTION DATE EXTENSION

         If the foregoing is acceptable, please execute a copy of this letter
agreement in the space provided and return such executed copy to the
undersigned.

                                                     Very truly yours,

                                                     SYSTEMONE TECHNOLOGIES INC.

                                                     By: /s/ Paul I. Mansur
                                                         ------------------
                                                     Paul I. Mansur
                                                     Chief Executive Officer

Agreed to an accepted as of the date first above written:

Holders:

ENVIRONMENTAL OPPORTUNITIES FUND II, L.P.       HANSEATIC AMERICAS LDC
ENVIRONMENTAL OPPORTUNITIES FUND II
(INSTITUTIONAL), L.P.                           By:  Hanseatic Corporation

By:  Fund II Mgt. Co., LLC                           By: /s/ Paul A. Biddelman
     General Partner                                     ---------------------
                                                     Paul A. Biddelman
                                                     President
         By: /s/ Bruce McMaken
             -----------------
         Bruce McMaken
         Manager

ENVIRONMENTAL OPPORTUNITIES FUND, L.P.

By:  Environmental Opportunities Management Co.,
     LLC
     General Partner

         By: /s/ Bruce McMaken
            ------------------
         Bruce McMaken
         Manager