Exhibit 10.15

                                 AMENDMENT NO. 4

            AMENDMENT  NO. 4 dated as of January __,  2000 to the Note  Purchase
Agreement referred to below, between:

            NUCO2 INC., a corporation  duly organized and validly existing under
      the laws of the State of Florida (the "Company");

            each of the Subsidiaries of the Company  appearing under the caption
      "SUBSIDIARY  GUARANTORS" on the signature pages hereto (each a "Subsidiary
      Guarantor" and, collectively,  the "Subsidiary Guarantors";  and, together
      with the Company, the "Obligors"); and

            each of the Investors appearing under the caption "INVESTORS" on the
      signature  pages  hereto  (each,  an  "Investor",  and  collectively,  the
      "Investors").

            WHEREAS,  the  Obligors  and the  Investors  are  party  to a Senior
Subordinated Note Purchase Agreement dated as of October 31, 1997 (as heretofore
modified and supplemented  and in effect on the date hereof,  the "Note Purchase
Agreement"), pursuant to which the Company issued (or will issue) its 12% Senior
Subordinated Notes in an aggregate  principal amount of up to $45,000,000 to the
Investors; and

            WHEREAS,  the parties to the Note Purchase  Agreement  wish to amend
the Note Purchase Agreement to make certain modifications thereto;

            Accordingly, the parties hereto hereby agree as follows:

            Section  1.  Definitions.   Except  as  otherwise  defined  in  this
Amendment No. 4, terms defined in the Note Purchase Agreement are used herein as
defined therein.

            Section 2.  Amendments  to Note Purchase  Agreement.  Subject to the
satisfaction  of the  conditions  precedent  specified  in Section 4 below,  but
effective as of the date hereof, the Note Purchase Agreement shall be amended as
follows:

            A.  References  in the Note Purchase  Agreement to "this  Agreement"
(and indirect references such as "hereunder",  "hereby",  "herein" and "hereof")
shall be deemed to be  references  to the Note  Purchase  Agreement  as  amended
hereby.

            B. Section 8.09 of the Note Purchase  Agreement  shall be amended in
its entirety to read as follows:

<PAGE>

                                      -2-


            "SECTION 8.09 Financial Covenants.

            (a)  Interest  Coverage  Ratio.  The  Company  will not  permit  the
Interest  Coverage Ratio to be less than the following  respective  ratios as at
the last day of each fiscal quarter during the following respective periods:

                      Period                              Ratio
                      ------                              -----

            From April 1, 1999
              through March 31, 2000                1.25 to 1.00

            From April 1, 2000
              through June 30, 2000                 1.50 to 1.00

            From July 1, 2000
              through September 30, 2000            1.65 to 1.00

            From October 1, 2000
              through December 31, 2000             1.75 to 1.00

            From January 1, 2001
              through March 31, 2001                2.00 to 1.00

            From April 1, 2001
              through June 30, 2001                 2.25 to 1.00

            From July 1, 2001
              through September 30, 2001            2.40 to 1.00

            From October 1, 2001
              and at all times thereafter           2.50 to 1.00

            (b) Total Net Funded  Debt  Coverage  Ratio.  The  Company  will not
permit  the  Total Net  Funded  Debt  Coverage  Ratio to  exceed  the  following
respective ratios at any time during the following respective periods:

                      Period                              Ratio
                      ------                              -----

            From October 1, 1999
              through December 31, 1999             5.50 to 1.00

            From January 1, 2000
              through March 31, 2000                5.00 to 1.00

<PAGE>
                                      -3-


            From April 1, 2000
              And at all times thereafter           4.50 to 1.00

            (c)  Minimum  Net Worth.  The  Company  shall at all times  maintain
      Consolidated  Net Worth of not less than the sum of (a)  $37,500,000,  (b)
      plus 50% of the cumulative Consolidated Net Income for each fiscal quarter
      ending on or after December 31, 1997 (but  specifically  not including any
      Consolidated Net Loss for any such fiscal quarter) plus (c) the cumulative
      net proceeds of all equity offerings (if any) made by the Company for each
      fiscal quarter ending on or after September 30, 1997."

            Section 3.  Representations  and Warranties.  The Company represents
and warrants to the Investors that: (i) the  representations  and warranties set
forth in Article VI of the Note Purchase  Agreement (as amended hereby) are true
and  complete  on the date hereof as if made on and as of the date hereof and as
if each  reference in said Article VI to "this  Agreement"  (or words of similar
import) referred to the Note Purchase Agreement as amended by this Amendment No.
4 (except that (x) certain of the  indebtedness  listed in Schedule  6.12 to the
Note  Purchase  Agreement  has been paid off by the  Company,  (y) the number of
validly  issued and  outstanding  shares of common  stock,  par value $0.001 per
share,  referred to in Section 6.13 of the Note Purchase  Agreement is 7,216,997
and (z) the number of  outstanding  options  granted under the  Company's  stock
option plans has changed); and (ii) no Default has occurred and is continuing.

            Section 4. Conditions Precedent. As provided in Section 2 above, the
amendments  to the Note  Purchase  Agreement  set forth in said  Section 2 shall
become effective,  as of the date hereof, upon the satisfaction of the following
conditions:

                        (a)  Amendment  No. 4. The execution and delivery of one
            or more counterparts of this Amendment No. 4 by the Obligors and the
            Required  Investors,  and receipt by the  Investors of evidence that
            the lenders party to the Senior Credit Agreement shall have approved
            this Amendment No. 4.

                        (b) Second Amendment to Senior Credit Agreement. Receipt
            by the  Investors  of a copy of the Second  Amendment  to the Senior
            Credit Agreement as executed by the parties thereto.

                        (c) Other  Documents.  Receipt by the  Investors of such
            other  documents  as any Investor or special New York counsel to the
            Investors may reasonably request.

            Section  5.  Miscellaneous.  Except  as  herein  provided,  the Note
Purchase  Agreement  shall remain  unchanged and in full force and effect.  This
Amendment  No. 4 may be  executed  in any number of  counterparts,  all of which
taken together shall  constitute one and the same amendatory  instrument and any
of the  parties  hereto may  execute  this  Amendment  No. 4 by signing any such
counterpart.  This  Amendment  No. 4 shall be  governed  by,  and  construed  in
accordance with, the law of the State of New York.


<PAGE>

            IN WITNESS  WHEREOF,  the parties  hereto have caused this Amendment
No. 4 to be duly  executed  and  delivered  as of the day and year  first  above
written.

                                   NUCO2 INC.


                                   By: /s/ Joann Sabatino
                                       ----------------------
                                   Title: CFO


                                   SUBSIDIARY GUARANTORS

                                   NUCO2 ACQUISITION CORP.


                                   By: /s/ Eric M. Wechsler
                                       ------------------------
                                    Title: Vice President


                                   KOCH COMPRESSED GASES, INC.


                                   By: /s/ Eric M. Wechsler
                                       ------------------------
                                     Title: Vice President


<PAGE>




                                   INVESTORS


                                   CHASE EQUITY ASSOCIATES, LLC
                                   (f/k/a Chase Equity Associates L.P.)

                                   By Chase Capital Partners,
                                    its Manager


                                   By: /s/ Richard D. Waters
                                       -------------------------
                                     Title: General Partner - Mezzanine


                                   DK ACQUISITION PARTNERS, L.P.

                                   By M.H. Davidson & Co.,
                                    its general partner


                                   By: _______________________
                                     Title:


                                   EMPIRE INSURANCE COMPANY,
                                   as executed on their behalf by
                                   their Investment Manager,
                                   Cohanzick Management, L.L.C.


                                   By_________________________
                                     Title:


                                   ORIX USA CORPORATION


                                   By:____________________
                                     Title:



<PAGE>




                                   PAINEWEBBER HIGH INCOME FUND,
                                   a series of PaineWebber Managed Investments
                                   Trust


                                   By:
                                     Title:

                                   SUNTRUST BANKS, INC.


                                   By: /s/ Robert Dudiak
                                       ---------------------
                                    Title: Group Vice President