<PAGE>

                                                         Exhibit 10.18

                               SUBLEASE AGREEMENT

      AGREEMENT made this 13th day of July, 1999, by and between The Image Bank,
Inc, a New York corporation with its principal office at 2777 Stemmons Freeway,
Suite 600, Dallas, TX 75207 (hereinafter "TIB" or "Sublessor") and
PaperExchange.com, a Delaware limited liability company with its principal
office at 545 Boylston Street, 8th Floor, Boston, MA 02116 (hereinafter
"Sublessee").

                                   WITNESSETH:

      WHEREAS, by Agreement of Lease dated as of July 31, 1998, by and between
Net Realty Holding Trust, c/o Net Properties Management, Inc., as landlord
(hereinafter called the "Landlord of the Underlying Lease") and Sublessor as
tenant, (hereinafter called the "Underlying lease"), a copy of which is annexed
hereto, made a part hereof and marked Exhibit "A," the said landlord did lease
to the said tenant certain premises located at 545 Boylston Street, 2nd Floor,
Boston, Massachusetts, as those particularly described in the Underlying Lease
(referred to in the underlying Lease as the "Premises"), and

      WHEREAS, Sublessor desires to sublease the Demised Premises (hereinafter
called the "Subleased Premises") to the Sublessee and the Sublessee is willing
to sublet the Subleased Premises from Sublessor on the conditions hereinafter
set forth,

      NOW, THEREFORE, in consideration of the mutual covenants and agreements
hereinafter set forth, it is hereby agreed by and between the parties hereto as
follows:

                                    ARTICLE 1

                               Subleased Premises

      Sublessor hereby subleases unto Sublessee, and Sublessee hereby takes and
hires from Sublessor, subject to the terms, conditions and provisions hereof,
the Subleased Premises which constitute all of the Premises described in said
Underlying Lease, together with any rights appurtenant to said Subleased
Premises granted to Sublessor in the Underlying Lease. Sublessee shall have all
the rights, privileges and benefits of the "Tenant" of such Underlying Lease
pertaining to the Subleased Premises except as herein specifically limited or
denied, and the same are hereby granted and conveyed to Sublessee from Sublessor
for the full term hereof.
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                                   ARTICLE II

                                      Term

      The term of this Sublease shall commence on July 13th, 1999 and terminate
on October 31, 2003 (the "Term").

                                   ARTICLE III

                           Rent, Taxes and Assessments

      Sublessee covenants and agrees to pay the following to Sublessor, at such
place or places as Sublessor may by notice in writing to Sublessee from time to
time direct, at the following taxes and times:

      (a) Base Rent. Base rent at the rate of Eight Thousand Seven Hundred
Seventy-Three and 33/100 Dollars ($8,773.33) payable each month in advance, on
the first day of each and every calendar month, commencing on August 1, 1999 and
prorated for the fraction of any month, without offset, deduction, notice or
demand.

      (b) Additional Rent. Sublessee shall pay to Sublessor, as additional rent,
all real estate taxes which Sublessor may be obligated to pay pursuant to the
terms of Article 6 of the Underlying Lease except that, for purposes of this
Sublease, Section 6(A)(2) shall be modified to read, "Base Tax Year" shall mean
the Fiscal Year 2000; any increases in Operating Expenses which Sublessor may be
obligated to pay pursuant to the terms of Article 7 of the Underlying Lease,
except that, for purposes of this Sublease, Section 7(A)(1) shall be modified to
read, "the term "Fiscal Base Year" shall mean Calendar Year 1999; and any other
charges which Sublessor may be obligated to pay pursuant to the Underlying Lease
during the term of this Sublease. The amounts due hereunder pursuant to the
aforesaid provisions of the Underlying Lease shall be payable to Sublessor no
less than ten (10) days prior to the date that Sublessor may be obligated to pay
same pursuant to the terms of said Underlying Lease.

      (c) All rent and additional rent shall be paid to Sublessor at the address
set forth above or such other address as Sublessor may designate in writing.
Sublessee shall forward its checks payable jointly to the Sublessor and the
Landlord of the Underlying Lease at least four business days prior to the due
date of any payments due herunder. Sublessor shall endorse and forward such
checks to the Landlord of the Underlying Lease promptly upon receipt.


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                                   ARTICLE IV

                                Security Deposit

Sublessee shall provide as security an irrevocable standby Letter of Credit in
the amount of Thirty-five Thousand Ninety-three and 34/100 U.S. Dollars
($35,093.34) with BankBoston N.A., 150 Federal Street, Boston, MA 02110 or other
institution acceptable to Sublessor upon execution of this Sublease. In the
event that, for any reason, the Letter of Credit can not be maintained,
Sublessee shall immediately pay to Sublessor the above sum in U.S. dollars to
serve as a Security Deposit. Failure to make such Security Deposit with
Sublessor shall be considered a default as set out in Article X, Default,
Section (a). This Security Deposit is security for the faithful performance and
observation by Sublessee of the terms, provisions and conditions of this lease;
it is agreed that in the event Sublessee defaults in respect of any of the
terms, provisions and conditions of this Sublease, including, but not limited
to, the payment of rent and additional rent, Sublessor may use, apply or retain
the whole or any part of the security to the extent required for the payment of
any rent, additional rent or any other sum as to which Sublessee is in default
or for any sum which Sublessor may expend or may be required to expend by reason
of Sublessee's default in respect of any of the terms, covenants and conditions
of this Sublease, including but not limited to, any damages or deficiency in the
reletting of the premises, whether such damages or deficiency accrued before or
after summary proceedings or other re-entry by Sublessor. In the event that
Sublessee shall fully and faithfully comply with all of the terms, provisions,
covenants and conditions of this Sublease, the security shall be returned to
Sublessee after the date fixed as the end of the Sublease and after delivery of
entire possession of the demised premises to Sublessor.

                                    ARTICLE V

                                       Use

      Sublessee shall have the right to use the Subleased Premises for the use
permitted by Article 9 of the Underlying Lease and for no other purpose.

                                   ARTICLE VI

                            Condition of the Premises

      Sublessee accepts the Subleased Premises in "as-is" condition.

      Sublessor shall deliver possession of the Subleased Premises to Sublessee
on July 13, 1999, subject to delays beyond Sublessor's reasonable control, but
in no event prior to the execution of this Sublease and the delivery of the
rental required hereunder.


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                                   ARTICLE VII

                            Assignment and Subletting

      Sublessee shall not have the right to assign Sublessee's interest in the
Sublease or sublease the Subleased Premises in whole or in part during the term
hereof, by operation of law or otherwise.

                                  ARTICLE VIII

                            Subordination of Sublease

      It is understood that the Sublessor is not the free owner of the Subleased
Premises, but has acquired its interest therein solely through the Underlying
Lease. This Sublease is subject to the provisions of the Underlying Lease and
subordinate thereto. In the event that the Underlying Lease shall be cancelled
or terminated, the term of this Sublease shall automatically terminate as of the
date of such cancellation or termination of the Underlying Lease and the
Sublessor shall not be liable in any way or to any extent to the Sublessee for
such termination or cancellation or for any damages or losses incurred or
claimed to be incurred by Sublessee as a result thereof.

                                   ARTICLE IX

                        Incorporation of Underlying Lease

      (a) Except as otherwise herein provided, this Sublease is subject to all
of the terms, covenants and conditions of the Underlying Lease and said terms,
covenants and conditions are incorporated herein by reference and made a part of
this Sublease as if fully set forth herein except as otherwise stated in Article
VIII, Paragraph (b) below. The words "Landlord" and "Tenant," as utilized in the
provisions of the Underlying Lease incorporated herein shall be deemed to refer
for the purposes of this Sublease, to Sublessor and Sublessee respectively and
the words "this lease" shall mean this Sublease. With respect to the Subleased
Premises, and only as between Sublessor and Sublessee, Sublessor shall have the
rights and obligations of the Landlord of the Underlying Lease as set forth in
the Underlying Lease, and Sublessee shall have the rights and obligations of the
tenant of the Underlying Lease as set forth in the Underlying Lease, except
where such rights and obligations are deleted, modified or adhered herein.

      (b) If any of the provisions of this Sublease are at variance or in
conflict with the provisions of the Underlying Lease due to a deletion,
modification or alteration of such provisions herein, the provisions of this
Sublease shall govern and control.


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      (c) Sublessee covenants that it will not commit, or suffer to be
committed, any act or act of omission in violation of the terms and provisions
of the Underlying Lease so as to render the Sublessor in default in any of the
terms, covenants and conditions of the Underlying Lease.

      (d) In the event of any default by the Landlord of the Underlying Lease
under the terms thereof, Sublessee shall give the Sublessor and the Landlord of
the Underlying Lease written notice thereof. Sublessor shall not be responsible
or liable for the failure by the Landlord of the Underlying Lease to furnish to
Sublessee any service or facility required under the Underlying Lease to be
furnished or provided and Sublessor will use its best efforts to compel the
Landlord of the Underlying Lease to cure any such default pursuant to the terms
of the Underlying Lease.

                                    ARTICLE X

                                     Default

      (a) In the event that Sublessee shall default in the payment of base rent
herein reserved and/or any additional rental when due, Sublessor shall notify
Sublessee in writing of such default, and Sublessee shall have five (5) days
from the date of such notice to cure such default.

      (b) In the event that Sublessee shall default in the performance of any
obligations hereunder when due, except the payment of base rent and/or
additional rent herein reserved, Sublessor shall notify Sublessee in writing of
such default, and Sublessee shall have twenty (20) days from the date of such
notice to cure such default.

      (c) Except in the event of a default, as provided in Subparagraphs (a) and
(b) set forth above:

            (i) whenever a time period is specified in the Underlying Lease
      within which the tenant therein must give notice or make a demand
      following an event, or within which said tenant must respond to any
      notice, request or demand previously given or made by the landlord, or
      comply with any obligation thereunder on such tenant's part, such time
      period is hereby changed (for purposes of this Sublease only) by
      subtracting ten (10) days therefrom; and

            (ii) whenever a time period is specified in the Underlying Lease
      within which the landlord must give notice or make a demand following an
      event or within which the landlord must respond to any notice, request or
      demand previously given or made by the tenant thereunder, or comply with
      any obligation thereunder on landlord's part, such time period is hereby
      changed (for purposes of this Sublease only) by adding ten (10) days
      thereto.


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It is the intent of this section to provide Sublessor with time within which to
transmit to the Landlord of the Underlying Lease any notices or demands received
by Sublessor from Sublessee, and to transmit to Sublessee any notices or demands
received by Sublessor from the Landlord of the Underlying Lease.

                                   ARTICLE XI

                               General Provisions

      (a) Any insurance required to be carried by Sublessee pursuant to the
provisions of the Underlying Lease as incorporated herein shall name the
Landlord of the Underlying Lease as well as Sublessor, as additional insured
parties and, if requested, any mortgage of the Underlying Landlord.

      (b) The purpose and intent of this Sublease is that the rental provided
for in Article III hereof shall be absolutely net to the Sublessor except as
expressly provided to the contrary herein. In this connection, Sublessor shall
not have any obligation to construct, maintain, alter or repair the Subleased
Premises or any facilities or improvements thereon or appurtenant thereto or be
obligated to provide Sublessee with any service or facility, but shall be
obligated only to use its best efforts to compel the Landlord of the Underlying
Lease to perform such duties if said Landlord has covenanted to do under the
terms of the Underlying Lease.

      (c) Sublessee shall, upon the request of Sublessor, subordinate this
Sublease to the lien of any present or future mortgage upon the Demised Premises
and/or the Subleased Premises irrespective of the time of execution or recording
of any such mortgage.

      (d) Sublessee shall not have any of the tenant's rights specified in the
provisions of Article 11 (Preparation of the Premises), Article 12
(Alterations), or Article 40 (Broker) of the Underlying Lease.

      (e) Any rights by the tenant to terminate the Underlying Lease provided
therein shall be exercised only by Sublessor when, in its sole opinion, those
conditions precedent required for a termination by tenant under the terms and
conditions of the Underlying Lease have occurred.

      (f) Sublessee shall pay for electricity for lights and plugs only at the
rate of $274.17 monthly ($3,290.00 per year) each month with the Base Rent,
notwithstanding any requirements in the Underlying Lease to pay for utilities.

      (g) Interior signage in the lobby directory and the floor directory for
Sublessee shall be provided at Sublessor's expense.


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                                   ARTICLE XII

                                     Brokers

Sublessee represents and warrants that there are no claims for brokerage
commissions or finder's fees, to the best of its knowledge and belief, in
connection with the execution of this Lease, and Sublessee agrees to indemnify
Sublessor and Landlord against and hold it harmless from all liabilities
including reasonable cost of counsel fees, arising out of discussions or
dealings of Sublessee with any broker. Sublessor shall pay the commission due to
its broker Peter Elliott, L.L.C., having an address at 260 Franklin Street,
Boston, Massachusetts 02110-3165, pursuant to a separate agreement between
Sublessor and its broker. Sublessee shall pay the commission due to its broker,
William J. Crean, having an address at One Financial Center, Boston,
Massachusetts 02111, pursuant to a separate agreement between Sublessee and its
broker.

                                  ARTICLE XIII

                                     Notices

      All notices or communications authorized or required hereunder shall be in
writing and shall be given by mailing the same be certified or registered mail,
return receipt requested, postage prepaid, and any such notice or communication
shall be deemed to have been given when received by the party to whom such
notice or communication shall be addressed. If intended for Sublessor, same
shall be mailed c/o Larry Horner, The Image Bank, Inc., 2777 Stemmons Freeway,
Suite 600, Dallas, TX 75207 and a copy to Elizabeth Warren at The Image Bank,
Inc. 2777 Stemmons Freeway, Suite 600, Dallas, TX 75207, or at such other
address as Sublessor may hereafter designate by notice to Sublessee, and if
intended for Sublessee, the same shall be mailed to Sublessee at 545 Boylston
Street, 8th Floor, Boston, MA 02116, or at such other address as Sublessee may
designate by notice to Sublessor.

                                   ARTICLE XIV

                               Merger Disclaimers

      All understandings and agreements heretofore had between the parties
hereto are merged in this Sublease, which alone fully and completely express
this Sublease, Sublessee has not relied upon or been induced by any statements
or representations, other than those expressly set forth in this Sublease, of
any person in respect of the title to or the physical condition of the Subleased
Premises, or any other manner affecting the Subleased Premises or this
transaction which might be pertinent in considering the execution of this
Sublease, Sublessee expressly acknowledges that no such representations not
embodied herein have been made.


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                                   ARTICLE XV

                          Entire Agreement and Benefit

      This agreement contains the entire understanding between the parties. No
waiver, change, modification or discharge of any of the provisions of this
Sublease shall be valid unless effected by an agreement in writing signed by
both parties hereto. The waiver of any of the provisions of this Sublease shall
not be deemed to be a waiver of any subsequent breach or default of the
provisions hereof. This Sublease shall be binding upon and inure to the benefit
of Sublessor and Sublessee and their respective successors and assigns.

                                   ARTICLE XVI

                                  Severability

      The illegality or invalidity of any provision of this Sublease, by reason
of any rule of law or public policy, shall not affect this Sublease or any other
provisions hereof, but this Sublease shall, nevertheless, remain in full force
and effect and shall be construed in all respects as if such invalid provision
were omitted.


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                                  ARTICLE XVII

                                  Construction

      This Sublease and the performance thereof shall be construed, regulated
and governed by the laws of the State of Massachusetts, where it has been made
and entered into. The section headings have been inserted for convenience only
and shall not enter into the interpretation or construction of this Sublease.

                                  Article XVIII

                           Condition to Effectiveness

This Sublease shall not become effective until the Sublessor has obtained the
Landlord of the Underlying Lease's written consent to this Sublease.

      IN WITNESS WHEREOF, the parties have hereunto set their hands and seals as
of the date and year first above written.

Sublessee:                              Sublessor:

PaperExchange.com                       The Image Bank, Inc.


By: /s/ Jason Weiss                     By:
   -------------------------------         -------------------------------
   Authorized signature                    Authorized signature

Printed Name: Jason Weiss               Printed Name:
             ---------------------                   ---------------------

Title: CEO                              Title:
      ----------------------------            ----------------------------


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