<PAGE>

                                                                   EXHIBIT 10.18

                               PURCHASE AGREEMENT

              THIS PURCHASE AGREEMENT, dated as of December 23, 2002 (this
"Agreement"), by and between VERTICALNET, INC., a Pennsylvania corporation (the
"Company"), and James Nolen (the "Holder").

                              W I T N E S S E T H:

              WHEREAS, the Holder is the owner of one or more Debentures (such
capitalized term and all other capitalized terms used in this Agreement having
the meanings provided in Section 1);

              WHEREAS, upon the terms and subject to the conditions of this
Agreement, the Holder wishes to exchange the Debentures with the Company for
shares of Common Stock and cash, and the Company wishes to issue shares of
Common Stock and pay cash to the Holder in exchange for the Debentures; and

              NOW THEREFORE, in consideration of the premises and the mutual
covenants contained herein and other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties hereto
agree as follows:

              1.    Definitions.

              (a)   As used in this Agreement, the terms "Agreement", "Company"
and "Holder" shall have the respective meanings assigned to such terms in the
introductory paragraph of this Agreement.

              (b)   All the agreements or instruments herein defined shall mean
such agreements or instruments as the same may from time to time be supplemented
or amended or the terms thereof waived or modified to the extent permitted by,
and in accordance with, the terms thereof and of this Agreement.

              (c)   The following terms shall have the following meanings (such
meanings to be equally applicable to both the singular and plural forms of the
terms defined):

              "Claims" means any losses, claims, damages, liabilities or
expenses (joint or several), incurred by a Person.

              "Closing Date" means 12:00 noon, New York City time, on December
31, 2002 or such other mutually agreed to time.

              "Common Stock" means the Common Stock, par value $0.01 per share,
of the Company.

              "Common Stock Equivalents" means any warrant, option, subscription
or purchase right with respect to shares of Common Stock, any security
convertible into, exchangeable for, or otherwise entitling the holder thereof to
acquire, shares of Common Stock

                                       -1-

<PAGE>

or any warrant, option, subscription or purchase right with respect to any such
convertible, exchangeable or other security.

              "Debentures" means $100,000.00 aggregate principal amount of the
Company's 5 1/4% Convertible Subordinated Debentures due 2004, owned by the
Holder and registered in the name of the Holder or its nominee.

              "DTC" means The Depository Trust Company.

              "Event of Default" shall have the meaning provided in the
Indenture.

              "Consideration" shall have the meaning provided in Section
2(a)(1).

              "Indemnified Person" means the Holder and each of its affiliates
and their respective officers, directors, stockholders and members and each
Person who controls the Holder within the meaning of the 1933 Act or the 1934
Act.

              "Indenture" means the Indenture, dated as of September 27, 1999,
between the Company and Deutsche Bank (as successor to Bankers Trust Company), a
New York banking corporation, as Trustee, relating to the Company's 5 1/4%
Convertible Subordinated Debentures due 2004.

              "1934 Act" means the Securities Exchange Act of 1934, as amended.

              "1933 Act" means the Securities Act of 1933, as amended.

              "Person" means any natural person, corporation, partnership,
limited liability company, trust, incorporated organization, unincorporated
association, or similar entity or any government, governmental agency or
political subdivision.

              "Principal Market" means the Nasdaq Smallcap Market or such other
U.S. market or exchange which is the principal market on which the Common Stock
is then listed for trading.

              "Rule 144" means Rule 144 under the 1933 Act or any other similar
rule or regulation of the SEC that may at any time provide a "safe harbor"
exemption from registration under the 1933 Act so as to permit a holder of any
securities to sell securities of the Company to the public without registration
under the 1933 Act.

              "SEC" means the Securities and Exchange Commission.

              "SEC Reports" means all annual reports, quarterly reports, proxy
statements and other reports filed by the Company under the 1934 Act, in each
case as filed with the SEC and including the information and documents (other
than exhibits) incorporated therein by reference.

              "Shares" means the shares of Common Stock issuable or issued in
exchange for the Debentures.

                                       -2-

<PAGE>

              "Short Sale" shall have the meaning given such term in Rule 3b-3
under the 1934 Act as in effect on the date of this Agreement.

              "Subsidiary" means any corporation or other entity of which a
majority of the capital stock or other ownership interests having ordinary
voting power to elect a majority of the board of directors or other persons
performing similar functions are at the time directly or indirectly owned by the
Company.

              "Trading Day" means a day on which the Principal Market is open
for the general trading of securities.

              "Violation" means

              (i)   any violation or alleged violation by the Company of the
         1933 Act, the 1934 Act, any state securities law or any rule or
         regulation under the 1933 Act, the 1934 Act or any state securities
         law, or

              (ii)  any breach or alleged breach by any Person other than the
         Holder of any representation, warranty, covenant, agreement or other
         term of this Agreement.

              2.    Agreement to Exchange; Exchange Value.

              (a)   The Purchase. Upon the terms and subject to the conditions
         of this Agreement,

              (1)   the Holder agrees to sell, assign, transfer and deliver the
          Debentures to the Company in exchange for the payment by the Company
          to the Holder of $16,000 in cash (the "Consideration"), and the
          Company agrees (A) to pay the Consideration in cash for the
          Debentures.

              (2)   The Holder has instructed the Company to make payment of the
          Consideration to the Holder's broker (the ":Broker"), and has agreed
          with the Broker to deliver the Debentures to the Company.

The Company agrees to cancel the Debentures in full immediately after the
closing.

              (b)   Closing. The closing of the exchange provided for in Section
2(a) shall occur on the Closing Date at the offices of the Company. At the
closing, upon the terms and subject to the conditions of this Agreement, (1) the
Company shall pay the Consideration to the Broker, on behalf of the Holder,
against delivery by the Broker, on behalf of the Holder, to the Company of the
Debentures in the manner provided in Section 2(c), and (2) the Holder shall
direct the Broker to deliver to the Company the Debentures against payment and
delivery by the Company to the Broker, on behalf of the Holder.

              (c)   Payment. Payment by the Company to the Holder on the Closing
Date of the Consideration shall be made by wire transfer of immediately
available funds at the closing on the Closing Date to:

                                       -3-

<PAGE>

              Bank: Jeffries & Company
              ABA No.

              For credit to account No. 391-01068
              For credit to the account of James A. Nolen.

              (d)   DTC Delivery. The transfer of the Debentures by the Holder
at the closing shall be made in accordance with Section 2.5(b)(2) of the
Indenture, in accordance with the applicable procedures of DTC. The Company
shall furnish to the Holder the name of the Company's broker who is a DTC
participant and account number prior to the closing, in order to effect such
delivery.

              3.    Representations, Warranties, Covenants, Etc. of the Holder.
The Holder represents and warrants to, and covenants and agrees with, the
Company as follows:

              (a)   Ownership of Securities. The Holder is the beneficial owner
of the Debentures and, upon consummation of the exchange of the Consideration
for the Debentures as provided in Section 2(a), will transfer and deliver to the
Company good title to the Debentures, free and clear of any lien or encumbrance.

              (b)   Authority. The execution, delivery and performance by the
Holder of this Agreement are within the powers of the Holder and have been duly
authorized by all necessary action on the part of the Holder. This Agreement
constitutes a valid and binding agreement of the Holder, enforceable against the
Holder in accordance with its terms, subject to the effect of any applicable
bankruptcy, insolvency, reorganization, moratorium or other similar laws now or
hereafter in effect relating to or affecting creditors' rights generally and
general principles of equity, regardless of whether such enforceability is
considered in a proceeding in equity or at law.

              4.    Representations, Warranties, Covenants, Etc. of the Company.
The Company represents and warrants to the Holder that the following matters are
true and correct on the date of execution and delivery of this Agreement, will
be true and correct on the Closing Date and the Company covenants and agrees
with the Holder as follows:

              (a)   Organization and Authority. The Company is a corporation
duly organized, validly existing and in good standing under the laws of the
Commonwealth of Pennsylvania and has all requisite corporate power and authority
(i) to own, lease and operate its properties and to carry on its business as
described in the SEC Reports and as currently conducted, and (ii) to execute,
deliver and perform its obligations under this Agreement and to consummate the
transactions contemplated hereby.

              (c)   Corporate Authorization. This Agreement has been duly and
validly authorized by the Company; this Agreement has been duly executed and
delivered by the Company and, assuming due execution and delivery by the Holder,
this Agreement is a valid and binding obligation of the Company enforceable in
accordance with its terms, subject to the effect of any applicable bankruptcy,
insolvency, reorganization, moratorium or other similar laws now or hereafter in
effect relating to or affecting creditors' rights generally and general
principles of equity, regardless of whether such enforceability is considered in
a proceeding in equity or at law.

                                       -4-

<PAGE>

              (d)   Non-contravention. The execution and delivery of this
Agreement by the Company and the consummation by the Company of the transactions
contemplated herein do not and will not, with or without the giving of notice or
the lapse of time, or both, (i) result in any violation of any provision of the
certificate of incorporation or by-laws or similar instruments of the Company or
any Subsidiary, (ii) conflict with or result in a breach by the Company or any
Subsidiary of any of the terms or provisions of, or constitute a default under,
or result in the modification of, or result in the creation or imposition of any
lien, security interest, charge or encumbrance upon any of the properties or
assets of the Company pursuant to, any indenture, mortgage, deed of trust or
other agreement or instrument to which the Company or any Subsidiary is a party
or by which the Company or any Subsidiary or any of their respective properties
or assets are bound or affected which would have a material adverse effect on
the business, properties, operations, condition (financial or other), results of
operations or prospects of the Company and the Subsidiaries, taken as a whole,
(iii) violate or contravene any applicable law, rule or regulation or any
applicable decree, judgment or order of any court, United States federal or
state regulatory body, administrative agency or other governmental body having
jurisdiction over the Company or any Subsidiary or any of their respective
properties or assets which would have a material adverse effect on the business,
properties, operations, condition (financial or other), results of operations or
prospects of the Company and the Subsidiaries, taken as a whole, or (iv) have
any material adverse effect on any permit, certification, registration,
approval, consent, license or franchise necessary for the Company or any
Subsidiary to own or lease and operate any of its properties and to conduct any
of its business or the ability of the Company or any Subsidiary to make use
thereof.

              (e)   Approvals, Filings, Etc. No authorization, approval or
consent of, or filing with, any court, governmental body, regulatory agency,
self-regulatory organization, or stock exchange or market or the stockholders of
the Company is required to be obtained or made by the Company or any Subsidiary
in connection with the execution, delivery and performance of this Agreement and
the issuance of the Shares as contemplated by this Agreement other than
application by the Company to the Principal Market for the listing of the
Shares.

              (i)   Absence of Brokers, Finders, Etc. No broker, finder, or
similar Person is entitled to any commission, fee, or other compensation by
reason of the transactions contemplated by this Agreement. The Company has not
and will not pay any commission or other remuneration for soliciting exchanges
of Debentures for Shares.

              5.    [this section intentionally left blank].

              6.    Conditions to the Company's Obligation to Close. The Holder
understands that the Company's obligation to issue and pay to the Holder the
Consideration in exchange for the Debentures on the Closing Date is conditioned
upon satisfaction of the following conditions precedent on or before the Closing
Date (any or all of which may be waived by the Company in its sole discretion):

              (a)   On the Closing Date, no legal action, suit or proceeding
shall be pending or threatened which seeks to restrain or prohibit the
transactions contemplated by this

                                       -5-

<PAGE>

Agreement; and

              (b)   The representations and warranties of the Holder contained
in this Agreement shall have been true and correct on the date of this Agreement
and on the Closing Date as if made on the Closing Date and on or before the
Closing Date the Holder shall have performed all covenants and agreements of the
Holder required to be performed by the Holder on or before the Closing Date.

              7.    Conditions to the Holder's Obligations to Close. The Company
understands that the Holder's obligation to exchange Debentures for the
Consideration on the Closing Date is conditioned upon satisfaction of the
following conditions precedent on or before the Closing Date (any or all of
which may be waived by the Holder in its sole discretion):

              (a)   On the Closing Date, no legal action, suit or proceeding
shall be pending or threatened which seeks to restrain or prohibit the
transactions contemplated by this Agreement;

              (b)   The representations and warranties of the Company contained
in this Agreement shall have been true and correct on the date of this Agreement
and shall be true and correct on the Closing Date as if given on and as of the
Closing Date (except for representations given as of a specific date, which
representations shall be true and correct as of such date), and on or before the
Closing Date the Company shall have performed all covenants and agreements of
the Company contained herein required to be performed by the Company on or
before the Closing Date;

              (c)   No Event of Default under and as defined in the Indenture or
event which, with the giving of notice or the passage of time, or both, would
constitute an Event of Default under and as defined in the Debentures shall have
occurred and be continuing;

              (d)   The Company shall have delivered to the Buyer a certificate,
dated the Closing Date, duly executed by its Chief Executive Officer or Chief
Financial Officer to the effect set forth in subparagraphs (a), (b), and (c) of
this Section 7;

              8.    Indemnification and Contribution.

              (a)   Indemnification. (1) To the extent not prohibited by
applicable law, the Company will indemnify and hold harmless each Indemnified
Person against any Claims to which any of them may become subject, insofar as
such Claims (or actions or proceedings, whether commenced or threatened, in
respect thereof) arise out of or are based upon any Violation or any of the
transactions contemplated by this Agreement; provided that the Company shall not
be liable under this provision to the extent that such Claims resulted from the
gross negligence or willful misconduct of the Indemnified Person. The Company
shall reimburse each such Indemnified Person, promptly as such expenses are
incurred and are due and payable, for any documented reasonable legal fees or
other documented and reasonable expenses incurred by them in connection with
investigating or defending any such Claim. Notwithstanding anything to the
contrary contained herein, the indemnification agreement contained in this
Section 8(a) shall not apply to amounts paid in settlement of any Claim if such
settlement is effected without the prior written consent of the Company, which
consent shall not be unreasonably withheld.

                                       -6-

<PAGE>

              (2)   Promptly after receipt by an Indemnified Person under this
Section 8(a) of notice of the commencement of any action (including any
governmental action), such Indemnified Person shall, if a Claim in respect
thereof is to be made against the Company under this Section 8(a), deliver to
the Company a notice of the commencement thereof and the Company shall have the
right to participate in, and, to the extent the Company so desires, to assume
control of the defense thereof with counsel reasonably satisfactory to the
Indemnified Person; provided, however, that an Indemnified Person shall have the
right to retain its own counsel with the fees and expenses to be paid by the
Company, if, in the reasonable opinion of counsel retained by the Company, the
representation by such counsel of the Indemnified Person and the Company would
be inappropriate due to actual or potential differing interests between such
Indemnified Person and any other party represented by such counsel in such
proceeding; provided further, however, that the Company shall not be responsible
for the fees and expenses of more than one separate counsel for all Indemnified
Persons hereunder and one separate counsel in each jurisdiction in which a Claim
is pending or threatened. The failure to deliver notice to the Company within a
reasonable time of the commencement of any such action shall not relieve the
Company of any liability to the Indemnified Person under this Section 8(a),
except to the extent that the Company is prejudiced in its ability to defend
such action. The indemnification required by this Section 8(a) shall be made by
periodic payments of the amount thereof during the course of the investigation
or defense, as such expense, loss, damage or liability is incurred and is due
and payable.

              (b)   Contribution. To the extent any indemnification by the
Company as set forth in Section 8(a) above is applicable by its terms but is
prohibited or limited by law, the Company agrees to make the maximum
contribution with respect to any amounts for which it would otherwise be liable
under Section 8(a) to the fullest extent permitted by law. In determining the
amount of contribution to which the respective parties are entitled, there shall
be considered the relative fault of each party, the parties' relative knowledge
of and access to information concerning the matter with respect to which the
Claim was asserted, the opportunity to correct and prevent any statement or
omission and any other equitable considerations appropriate under the
circumstances; provided, however, that (a) no contribution shall be made under
circumstances where the maker would not have been liable for indemnification
under the fault standards set forth in Section 8(a) and (b) no Person guilty of
fraudulent misrepresentation (within the meaning of Section 11(f) of the 1933
Act) shall be entitled to contribution from any other Person who was not guilty
of such fraudulent misrepresentation.

              (c)   Other Rights. The indemnification and contribution provided
in this Section shall be in addition to any other rights and remedies available
at law or in equity.

              9.    Miscellaneous.

              (a)   Governing Law. THIS AGREEMENT SHALL BE GOVERNED BY AND
INTERPRETED IN ACCORDANCE WITH THE LAWS OF THE COMMONWEALTH OF PENNSYLVANIA.

              (b)   Headings. The headings, captions and footers of this
Agreement are for convenience of reference and shall not form part of, or affect
the interpretation of, this Agreement.

                                       -7-

<PAGE>

              (c)   Severability. If any provision of this Agreement shall be
invalid or unenforceable in any jurisdiction, such invalidity or
unenforceability shall not affect the validity or enforceability of the
remainder of this Agreement or the validity or enforceability of this Agreement
in any other jurisdiction.

              (d)   Notices. Any notices required or permitted to be given under
the terms of this Agreement shall be in writing and shall be sent by mail,
personal delivery, by telephone line facsimile transmission or courier and shall
be effective five days after being placed in the mail, if mailed, or upon
receipt, if delivered personally, by telephone line facsimile transmission or by
courier, in each case addressed to a party at such party's address (or telephone
line facsimile transmission number) shown in the introductory paragraph or on
the signature page of this Agreement or such other address (or telephone line
facsimile transmission number) as a party shall have provided by notice to the
other party in accordance with this provision. In the case of any notice to the
Company, such notice shall be addressed to the Company at its address (or
telephone line facsimile transmission number) shown on the signature page
hereto, Attention: Chief Executive Officer, with a copy addressed to the General
Counsel, and in the case of any notice to the Holder, such notice shall be
addressed to the Holder at its address (or telephone line facsimile transmission
number) shown on the signature page hereto and a copy shall be given to General
Counsel of the Holder.

              (e)   Counterparts. This Agreement may be executed in counterparts
and by the parties hereto on separate counterparts, each of which shall be
deemed to be an original but all of which together shall constitute one and the
same instrument. A telephone line facsimile transmission of this Agreement
bearing a signature on behalf of a party hereto shall be legal and binding on
such party. Although this Agreement is dated as of the date first set forth
above, the actual date of execution and delivery of this Agreement by each party
is the date set forth below such party's signature on the signature page hereof.
Any reference in this Agreement or in any of the documents executed and
delivered by the parties hereto in connection herewith to (1) the date of
execution and delivery of this Agreement by the Holder shall be deemed a
reference to the date set forth below the Holder's signature on the signature
page hereof, (2) the date of execution and delivery of this Agreement by the
Company shall be deemed a reference to the date set forth below the Company's
signature on the signature page hereof and (3) the date of execution and
delivery of this Agreement, or the date of execution and delivery of this
Agreement by the Holder and the Company, shall be deemed a reference to the
later of the dates set forth below the signatures of the parties on the
signature page hereof.

              (f)   Entire Agreement; Benefit. This Agreement constitutes the
entire agreement between the parties hereto with respect to the subject matter
hereof. There are no restrictions, promises, warranties, or undertakings, other
than those set forth or referred to herein and therein. This Agreement
supersedes all prior agreements and understandings, whether written or oral,
between the parties hereto with respect to the subject matter hereof. This
Agreement and the terms and provisions hereof are for the sole benefit of only
the Company, the Holder and their respective successors and permitted assigns
and in no event shall the Holder have any liability to any stockholder or
creditor of the Company or any other Person (other than the Company) in any way
relating to or arising from this Agreement or the transactions contemplated
hereby.

                                       -8-

<PAGE>

              (g)   Waiver. Failure of any party to exercise any right or remedy
under this Agreement or otherwise, or delay by a party in exercising such right
or remedy, or course of dealing between the parties, shall not operate as a
waiver thereof or an amendment hereof, nor shall any single or partial exercise
of any such right or power, or any abandonment or discontinuance of steps to
enforce such a right or power, preclude any other or further exercise thereof or
exercise of any other right or power.

              (h)   Amendment. No amendment, modification, waiver, discharge or
termination of any provision of this Agreement nor consent to any departure by
the Holder or the Company therefrom shall in any event be effective unless the
same shall be in writing and signed by the party to be charged with enforcement,
and then shall be effective only in the specific instance and for the purpose
for which given. No course of dealing between the parties hereto shall operate
as an amendment of this Agreement.

              (i)   Best Efforts. Each of the parties shall use its best efforts
timely to satisfy each of the conditions to the other party's obligations set
forth in Section 6 or 7, as the case may be, of this Agreement on or before the
Closing Date.

              (j)   Further Assurances. Each party to this Agreement will
perform any and all acts and execute any and all documents as may be necessary
and proper under the circumstances in order to accomplish the intents and
purposes of this Agreement and to carry out its provisions.

              (k)   Expenses. The Company and the Holder shall each be
responsible for their expenses (including, without limitation, the legal fees
and expenses of its counsel), except as otherwise specifically provided in this
Section 9(j), incurred by them in connection with the negotiation and execution
of, and closing under, this Agreement and of the transactions contemplated
hereby. If the closing under this Agreement shall have occurred, then the
Company shall pay or reimburse the Holder for one-half of its reasonable legal
fees and expenses relating to this Agreement, not to exceed $10,000 to be paid
by the Company. The Company shall pay on demand all expenses incurred by the
Holder after the Closing Date, including reasonable fees and disbursements of
counsel, as a consequence of, or in connection with (1) any default or breach of
any of the Company's obligations set forth in this Agreement and (2) the
enforcement or restructuring of any right of, including the collection of any
payments due, the Holder under this Agreement, including any action or
proceeding relating to such enforcement or any order, injunction or other
process seeking to restrain the Company from paying any amount due the Holder.

              (l)   Termination. The Holder shall have the right to terminate
its obligation to exchange the Debenture under this Agreement by giving notice
to the Company at any time at or prior to the closing or Closing Date if:

              (1)   the Company shall have failed, refused, or been unable at or
         prior to the date of such termination of this Agreement to perform any
         of its material obligations hereunder;

                                       -9-

<PAGE>

              (2)   any other material condition of the Holder's obligations
         hereunder is not fulfilled; or

              (3)   the closing shall not have occurred on a Closing Date on or
         before December 31, 2002, other than solely by reason of a breach of
         this Agreement by the Holder.

Any such termination shall be effective upon the giving of notice thereof by the
Holder. Upon a termination under Section 9(l)(1) or (3), the Holder shall have
no further obligation to the Company.

              (m)   Survival. The respective representations, warranties,
covenants and agreements of the Company and the Holder contained in this
Agreement and the documents delivered in connection with this Agreement shall
survive the execution and delivery of this Agreement and the closing hereunder,
and shall remain operative and in full force and effect regardless of any
investigation made by or on behalf of the Holder or any Person controlling or
acting on behalf of the Holder or by the Company or any Person controlling or
acting on behalf of the Company.

              (n)   Public Statements, Press Releases, Etc. The Company and the
Holder shall have the right to approve before issuance any press releases or any
other public statements with respect to the transactions contemplated hereby;
provided, however, that the Company shall be entitled, without the prior
approval of the Holder, to make any press release or other public disclosure
with respect to such transactions as is required by applicable law and
regulations, including the 1934 Act and the rules and regulations promulgated
thereunder (although the Holder shall be consulted by the Company in connection
with any such press release or other public disclosure prior to its release and
shall be provided with a copy thereof).

              (o)   Construction The language used in this Agreement will be
deemed to be the language chosen by the parties to express their mutual intent,
and no rules of strict construction will be applied against any party.

                [Remainder of this Page Intentionally Left Blank]

                                      -10-

<PAGE>

              IN WITNESS WHEREOF, the parties have caused this Agreement to be
duly executed by their respective officers or other representatives thereunto
duly authorized as of the date first set forth above and on the dates set forth
below their respective signatures.

                                VERTICALNET, INC.



                                By: /s/ Nathanael V. Lentz
                                   -------------------------------------
                                   Name:
                                   Title:

                                Address:

                                300 Chester Field Parkway
                                Malvern, Pennsylvania 19355

                                Facsimile No.: (610) 240- 9470

                                Date: December 23, 2002



                                By: /s/ James A. Nolen
                                   -------------------------------------
                                   Name: James A. Nolen, 3/rd/
                                   Title:

                                Address:

                                Facsimile No.:
                                Date: December 23, 2002

                                      -11-