<PAGE>
 
                                                                    EXHIBIT 4.18

     THE SECURITIES REPRESENTED BY THIS AGREEMENT HAVE NOT BEEN REGISTERED UNDER
THE SECURITIES ACT OF 1933, AS AMENDED, THE OKLAHOMA SECURITIES ACT OR THE
SECURITIES LAWS OF ANY OTHER STATE.  THE SECURITIES HAVE BEEN ACQUIRED FOR
INVESTMENT AND MAY NOT BE SOLD OR TRANSFERRED FOR VALUE IN THE ABSENCE OF AN
EFFECTIVE REGISTRATION OF THEM UNDER THE SECURITIES ACT OF 1933, AS AMENDED,
AND/OR THE SECURITIES LAWS OF ANY OTHER STATE OR AN OPINION OF COUNSEL OR OTHER
DOCUMENTATION SATISFACTORY TO APPLIED INTELLIGENCE GROUP, INC. THAT SUCH
REGISTRATION IS NOT REQUIRED UNDER SUCH ACT OR ACTS.


                            STOCK OPTION AGREEMENT

                       OPTIONS TO PURCHASE COMMON STOCK

                                      OF

                              THE VIALINK COMPANY
                  (FORMERLY APPLIED INTELLIGENCE GROUP, INC.)

                      Effective Date:  December 19, 1998


     This is to certify that, for value received, Roger Lockhart (an assignee of
John Simonelli) or any subsequent holder or holders of option rights hereunder
by virtue of assignment or transfer (the "Holder") is entitled to purchase,
subject to the provisions of this Stock Option (this "Option"), from The Vialink
Company (formerly Applied Intelligence Group, Inc.), an Oklahoma corporation
(the "Company"), up to THIRTY THOUSAND (30,000) shares of Common Stock, $.001
par value, of the Company (the "Stock") at an exercise price of FIVE AND NO/100
DOLLARS ($5.00) per share (the "Exercise Price"). With the exception of any
adjustments pursuant to Section 4 of this Option, the Stock issuable upon
exercise of this Option shall be in all respects identical to the Common Stock
issued and outstanding of the Company as of the date hereof.  The shares of
Stock or other securities deliverable upon such exercise, as adjusted from time
to time, are hereinafter sometimes referred to as the "Option Securities."
Unless the context otherwise requires, the term "Option" or "Options" as used
herein includes this Option and any other Option or Options that may be issued
pursuant to the provisions of this Stock Option Agreement (this "Agreement"),
whether upon transfer, assignment, partial exercise, divisions, combinations,
exchange or otherwise, and the term "Holder" or "Holders" includes any
registered transferee or transferees or registered assignee or assignees of
Holder, who in each case shall be subject to the provisions of this Option, and
when used with reference to Option Securities, means the holder or holders of
such Option Securities.

     SECTION 1.  Exercise of Option.  Subject to the provisions of this
Agreement, the Holder shall be eligible to exercise that portion of this Option
for purchase of the number of Option Securities on or before the Expiration Date
(as defined below). This Option may be exercised in whole or in part at any time
or from time to time during the period commencing two years following completion
by the Company's the initial public offering of common stock and redeemable
common stock purchase warrants and then only in the event the initial public
offering is completed on or before December 31, 1996 (the "Commencement Date"),
and ending 5:00 P.M., Central Daylight-Savings Time, on  November 30, 2001 (the
"Expiration Date"), by presentation and surrender to Company at its principal
office of this Option and the Purchase Form annexed hereto, duly executed and
accompanied by payment, in cash, certified or official bank check payable to the
order of Company in the amount of the Exercise Price for the number of shares of
Stock (or Option Securities) specified in such Form. In the event Company fails
to complete the initial public offering of its common stock on or before
December 31, 1996, this Agreement and this Option shall terminate. Upon such
exercise, Company shall issue to the Holder one or more certificates for the
shares of Stock (or Option Securities), as appropriate.  If this Option is
exercised in part only, Company shall, promptly after presentation of this
Option upon such exercise, execute and deliver a new Option evidencing the
rights of Holder thereof to purchase the balance of the shares of Stock (or
Option Securities) purchasable hereunder upon the same terms and conditions as
herein set forth.
<PAGE>
 
     SECTION 2.  Reservation of Shares.  Company shall at all times after the
date hereof and until expiration or full exercise of this Option reserve for
issuance and delivery upon exercise of this Option the number of Option
Securities as shall be required for issuance and delivery upon exercise of this
Option.

     SECTION 3.  Transfer, Exchange, Assignment or Loss of Option.

     SECTION 3.1  Transferability.  This Option may be assigned or transferred,
in whole or in part, as provided herein so long as such assignment or transfer
is in accordance with and subject to the provisions of the Securities Act of
1933, as amended, and the rules and regulations promulgated thereunder (said Act
and such rules and Regulations being hereinafter collectively referred to as the
"Securities Act").  Any purported transfer or assignment made other than in
accordance with this Section 3 shall be null and void and of no force and
effect.

     SECTION 3.2  Transfer Procedure.  Any assignment permitted hereunder shall
be made by surrender of this Option to Company at its principal office with the
Assignment Form annexed hereto duly executed and funds sufficient to pay any
transfer tax.  In such event Company shall, without charge, execute and deliver
a new Option in the name of the assignee named in such instrument of assignment
and designate the assignee as the registered holder on the Company's records and
this Option shall promptly be canceled.  This Option may be divided or combined
with other Options which carry the same rights upon presentation thereof at the
principal office of Company together with a written notice signed by Holder
hereof, specifying the names and denominations in which new Options are to be
issued.

     SECTION 3.3  Loss or Destruction of this Agreement.  Upon receipt by
Company of evidence satisfactory to it of the loss, theft, destruction or
mutilation of this Option, and (in the case of loss, theft or destruction) of
reasonably satisfactory indemnification to Company or (in the case of
mutilation) presentation of this Option for surrender and cancellation, Company
will execute and deliver a new Option of like tenor and date and any such lost,
stolen, destroyed or mutilated Option shall thereupon become void.  This Option
may be exchanged at the option of the Holder for another Option or Options of
different denominations, of like tenor and evidencing in the aggregate the
number of shares of Stock or Option Securities purchasable pursuant to this
Option, upon surrender of this Option, with the Assignment Form duly filled in
and executed, to the Company at its principal office, at any time or from time
to time after the close of business on the date hereof and prior to the close of
business on the Expiration Date.  The Company shall promptly cancel the
surrendered Option and deliver the new Option or Options pursuant to the
provisions of this Section.

     SECTION 4.  Adjustment in the Number, Kind and Price of Option Securities.
The number and kind of Option Securities purchasable upon exercise of this
Option shall be subject to adjustment from time to time upon the occurrence,
after the date hereof, of the following events:

     SECTION 4.1  Stock Dividends and Splits.  In the event Company shall (i)
pay a dividend in, or make a distribution of, shares of Stock or of capital
stock convertible into Stock on its outstanding Stock, (ii) subdivide (forward
split) its outstanding shares of Stock into a greater number of such shares, or
(iii) combine (reverse split) its outstanding shares of Stock into a smaller
number of such shares, the total number of shares of Stock purchasable upon the
exercise of this Option immediately prior thereto shall be adjusted so that the
Holder shall be entitled to receive at the same Exercise Price the number of
shares of Stock and the number of shares of capital stock convertible into Stock
which such Holder would have owned or have been entitled to receive immediately
following the happening of such event, assuming and giving effect to the
exercise of this Option by such Holder.  Any adjustment made pursuant to this
Subsection shall, in the case of a stock dividend or distribution or a stock
issuance, become effective as of the record date therefor and, in the case of a
subdivision or combination, be made as of the effective date thereof.

     SECTION 4.2  Adjustment of Option Securities.  In the event of any
adjustment of the total number of shares of Stock purchasable upon the exercise
of this Option pursuant to Subsection 4.1, the Exercise Price shall remain
unchanged, but the number of shares of capital stock or Option Securities
obtainable on exercise of this Option shall be adjusted as provided in
Subsection 4.1.

                                       2
<PAGE>
 
     SECTION 4.3  Reorganization, Recapitalization, etc.  In the event of a
capital reorganization or a reclassification of the Stock (except as provided in
Subsection 4.1 or Subsection 4.4), the holder of this Option, upon exercise
thereof, shall be entitled to receive, in lieu of the Stock to which he would
have become entitled upon exercise immediately prior to such reorganization or
reclassification, the shares (of any class or classes) or other Option
Securities or property of the Company (or cash) that the Holder would have been
entitled to receive at the same Exercise Price upon such reorganization or
reclassification if this Option had been exercised immediately prior thereto;
and in any such case, appropriate provision shall be made for the application of
this Section 4 with respect to the rights and interests thereafter of the Holder
of this Option (including, but not limited to, the allocation of the Exercise
Price between or among the Option Securities), to the end that this Section 4
(including the adjustments of the number of shares of Stock or other Option
Securities purchasable) shall thereafter be reflected, as nearly as reasonably
practicable, in all subsequent exercises of this Option for any shares or other
Option Securities or other property (or cash) thereafter deliverable upon the
exercise of this Option.

     SECTION 4.4  Consolidation, Merger, etc.  In case of any consolidation of
the Company with, or merger of the Company with, or merger of the Company into,
another corporation (other than a consolidation or merger which does not result
in any reclassification or change of the outstanding Stock), or in case of any
sale or conveyance to another corporation of the property of the Company as an
entirety or substantially as an entirety, the corporation formed by such
consolidation or merger or the corporation which shall have acquired such
assets, as the case may be, shall execute and deliver to the Holder a supplement
to this Option or a new option providing that the Holder of this Option shall
have the right thereafter (until the Expiration Date) to receive, upon exercise
of this Option or any new option, at the same Exercise Price, solely the kind
and amount of shares of Option Securities and property (or cash) receivable upon
such consolidation, merger, sale or transfer by the Holder of this Option for
the number and kind of Option Securities for which this Option might have been
exercised immediately prior to such consolidation, merger, sale or transfer.
Such supplemental option or new option shall provide for adjustments which shall
be as nearly equivalent as may be practicable to the adjustments provided in
this Section.  The above provision of this Subsection 4.4 shall similarly apply
to successive consolidations, mergers, sales or transfers.

     SECTION 4.5  Notification of Adjustment.  Whenever the Option Securities
purchasable upon exercise of this Option are modified as provided in Section 4.1
or 4.4, the Company will promptly deliver to the Holder a certificate signed by
the Chairman of the Board, Chief Executive Officer or the President, or a Vice
President of the Company and by the Treasurer or an Assistant Treasurer or the
Secretary or an Assistant Secretary of the Company setting forth the number and
kind of Option Securities purchasable and the other property (including cash)
receivable by the Holder upon exercise of this Option or any supplemental or new
option.  Such certificate will state that such adjustments in the kind of
purchasable Option Securities and other property (including cash) receivable by
the Holder upon exercise of this Option conform to the requirements of this
Section 4, and setting forth a brief statement of the facts accounting for such
adjustments.  In the event, the Holder of this Option does not agree with such
determination of the Board of Directors of the Company as set forth in the
certificate, the Company shall retain a firm of independent public accountants
acceptable to the Holder to make any computation required under this Section 4,
and a certificate signed by such firm shall be conclusive evidence of the
correctness of any computation made under this Section 4.

     SECTION 5.  Redemption and Dividend Consent Requirements.  This Option may
not be redeemed by Company.  During the period from the date hereof until
exercise of this Option in full or through the Expiration Date, the Company
shall not declare any dividends payable in cash or property (other than in
liquidation, voluntary or involuntary dissolution or winding-up of the Company)
without the prior written consent of the Holder of this Option.

     SECTION 6.  Notice of Certain Corporation Action.  In case the Company
after the date hereof shall propose to effect any consolidation or merger to
which the Company is a party and for which approval of any shareholders of the
Company is required, or any sale, transfer or other disposition of its property
and assets substantially as an entirety, or the liquidation, voluntary or
involuntary dissolution or winding-up of the Company, then, in each such case,
the Company shall mail (by first-class, postage prepaid mail) to the Holder of
this Option notice of such proposed action, 

                                       3
<PAGE>
 
which notice shall specify the date on which such reclassification,
reorganization, consolidation, merger, sale, transfer, other disposition,
liquidation, voluntary or involuntary dissolution or winding-up shall take place
or commence, as the case may be, and which shall also specify any record date
for determination of holders of the capital stock of the Company entitled to
vote thereon or participate therein and shall set forth such facts with respect
thereto as shall be reasonably necessary to indicate any adjustments in the
number or kind of Option Securities purchasable upon exercise of this Option
which will be required as a result of such action, and the Holder may thereafter
exercise this Option. Such notice shall be filed and mailed in the case of any
action covered by this Section 6, at least 20 days prior to the earlier of (i)
the date on which such reclassification, reorganization, consolidation, merger,
sale, transfer, other disposition, liquidation, voluntary or involuntary
dissolution or winding-up is expected to become effective, (ii) the date on
which it is expected that holders of shares of the capital stock of record on
such date shall be entitled to exchange their shares for securities or other
property deliverable upon such reclassification, reorganization, consolidation,
merger, sale, transfer, other disposition, liquidation, voluntary or involuntary
dissolution or winding-up, or (iii) the record date for determination of holders
of the capital stock of the Company entitled to vote on such action or
participate in such action. Failure of the Holder to exercise this Option in
whole or in part prior to any corporate action as described in this Section 6
shall not affect or alter the rights of the Holder as set forth in this Option.

     SECTION 7.  Acquisition for Investment Purposes.  The Holder represents and
acknowledges to the Company and its officers and directors that the Option
Securities at the time of issuance to the Holder upon exercise of this Option
(i) will be acquired by the Holder for investment purposes only without the
intent to resell such Option Securities, (ii) will be issued pursuant to
exemption from registration under the Securities Act and any applicable state
securities act, (iii) will not be transferred except pursuant to registration
under the Securities Act and any applicable state securities act unless pursuant
to exemption from registration under such acts, and (iv) the certificates
evidencing the Option Securities will bear appropriate restrictive transfer
legends as required pursuant to the Securities Act and any applicable state
securities act.

     SECTION 8.  Registration under Securities Act.

     SECTION 8.1  Right to Include Option Securities.  In the event the Company
at any time amends a  registration statement pursuant to a post-effective
amendment under the Securities Act of 1933, as amended (the "Securities Act"),
proposes to registered any of its securities under the Securities Act (other
than by registration on Form S-8 or Form S-4 or any successor or similar form),
whether or not for sale for the Company's own account, each such time the
Company will give prompt written notice (the "Registration Notice") to all
Holders of Option Securities of the Company's intention to register its
securities under the Securities Act, of the intended method of disposition of
such securities, and of such Holder's or Holders' rights under this Section 8.1.
Upon the written request of any such Holder made within 15 days after the
receipt of such Registration Notice (which request shall specify the Option
Securities intended to be disposed of by such Holder and the intended method of
disposition thereof, which can be by an underwritten offering, even if such was
not intended by the Company), subject to the provisions of this Agreement, the
Company will use its best efforts to effect the registration under the
Securities Act which the Company has been requested to register by a Holder or
Holders of Option Securities to the extent necessary to permit the disposition
in accordance the intended method or methods of the Option Securities to be
registered.

     SECTION 8.2  Priorities of Underwriter or Company.

     SECTION 8.2.1  Underwritten Registration.  In the event (i) a registration
pursuant to Section 8 involves an underwritten offering of securities so being
registered, whether or not for sale for the account of the Company, to be
distributed by or through one or more underwriters under underwriting terms
appropriate for such a transaction, (ii) the Option Securities so requested to
be registered for sale for the account of a Holder or Holders of Option
Securities are not also to be included in such underwritten offering (because
the Company has not been requested so to include such Option Securities pursuant
to Section 8.1 hereof), and (iii) the managing underwriter of such underwritten
offering shall inform the Company and the Holder or Holders of Option Securities
requesting such registration in writing of its belief that the number of
securities requested to included in such registration exceeds the number which
can be sold in (or 

                                       4
<PAGE>
 
during the time of) such offering, then the Company may include all securities
proposed by the Company to be sold for its own account and may decrease the
number of Option Securities so proposed to be sold and so requested to be
included in such registration by the Holder (or the Holders on a pro rata on the
basis determined by dividing the number of shares of Option Securities requested
to included in the registration by the Holders of such Option Securities by the
total number of such Option Securities to be included in such registration
statement) to the extent necessary to reduce the number of securities to be
included in the registration to the level recommended by the managing
underwriter.

     SECTION 8.2.2  Company's Right to Delay Registration.  In the event, at any
time after giving the applicable Registration Notice pursuant to Section 8.1 and
prior to the effective date of the registration statement or amendment thereto
under the Securities Act is filed in connection with such registration, the
Company shall determine for any reason, after consultation with the Holder or
Holders of Option Securities which have requested inclusion in such
registration, not to register or to delay registration of such Option
Securities, the Company may, at its election, give written notice of such
determination to each such Holder of Option Securities and, thereupon, (i) in
the case of a determination not to register, the Company shall be relieved of
its obligation to register any Option Securities in connection with such
registration; provided, however, that such determination by the Company shall be
without prejudice to the rights of any Holder or Holders of Option Securities
pursuant to Section 8 hereof to include such Holder's or Holders' Option
Securities in a subsequent registration by the Company, and (ii) in the case of
a determination by the Company to delay registering, the Company shall be
permitted to delay registering any Option Securities for the same period as the
delay in registering such other securities.  The Company will pay all
registration expenses in connection with each registration of Option Securities
requested pursuant to Section 8 hereof.

     SECTION 8.3  Registration Procedures.  Whenever the Company is required to
used its best efforts to effect the registration of any Option Securities under
the Securities Act as provided in Section 8 hereof, the Company, as
expeditiously as possible, will undertake and perform the following:

          (i)  with respect to the registration of Option Securities under the
     Securities Act prepare and (as soon thereafter as possible) file with the
     United States Securities and Exchange Commission (the "Commission") the
     requisite registration statement or amendment to effect such registration
     and, thereafter, use its best efforts to cause such registration or
     amendment to become effective; provided however, that the Company may
     discontinue any registration of its securities which are not Option
     Securities at any time prior to the effective date of the registration
     statement or amendment under the Securities Act or under any state
     securities or blue sky laws relating thereto;

          (ii)  prepare and file with the Commission which amendments and
     supplements to the requisite registration statement and the prospectus used
     in connection therewith as may be necessary to keep such registration
     statement effective and to comply with the provisions of the Securities Act
     with respect to the disposition of all securities covered by such
     registration statement until such time that all of such securities have
     been disposed of in accordance with the intended methods of disposition by
     the seller or sellers thereof as set forth in such registration statement,
     but in no event for a period which would exceed 180 days from the date on
     which the registration statement or amendment became effective under the
     Securities Act;

          (iii)  furnish to each seller of Option Securities covered by such
     registration statement (A) such number of conformed copies of such
     registration statement and such number of each amendment and supplement
     thereto (in each case including all exhibits), (B) such number of copies of
     the prospectus contained in such registration statement (including
     preliminary prospectus and any summary prospectus) and any other prospectus
     filed under Rule 424 under the Securities Act, in 

                                       5
<PAGE>
 
     conformity with the requirements of the Securities Act, and (C) such other
     documents, as such seller may reasonably request;

          (iv)  use its best efforts to register or qualify all Option
     Securities and other securities covered by such registration statement
     under such other securities or blue sky laws of each state that each Holder
     of Option Securities shall reasonably request, to keep such registration or
     qualification in effect for so long as such registration statement remains
     in effect (subject to Section 8.3(ii)), and take any other action which may
     be reasonably necessary or advisable to enable such seller to consummate
     the disposition in such states of the securities owned by such seller,
     except that the Company shall not for any such purpose be required to
     either qualify generally to do business as a foreign corporation, or
     subject itself to taxation in any jurisdiction wherein it would not, but
     for the requirements of this subsection (iv), be obligated to be so
     qualified or subject to taxation or to any material restrictions on the
     conduct of the Company's business, or any restrictions on payments to any
     of the Company's shareholders, or require the escrow, "lockup" or placing
     of any restrictions on the sale and disposition of securities of the
     Company (other than as may have been previously imposed or existed
     immediately before the effective date of the registration statement under
     the Securities Act) held of record by any of the Company's officers,
     directors or controlling persons that is not a Holder of Option Securities;

          (v)  use its best efforts to cause all Option Securities covered by
     such registration statement to be registered with or approved by such other
     federal or state governmental agencies or authorities as may be necessary
     to enable the seller or sellers thereof to consummate the disposition of
     such Option Securities;

          (vi)  furnish to each Holder of Option Securities covered by the
     registration statement a signed counterpart, addressed to each Holder (and
     the underwriters, if any) of

                 (A)  an opinion of counsel for the Company, dated the effective
          date of such registration statement (and, if such registration
          includes an underwritten offering, dated the date of the closing under
          the underwriting agreement) reasonably satisfactory in form and
          substance to such seller, and

                 (B)  in the event the offering is underwritten, a "comfort"
          letter, dated the effective date of such registration statement (and,
          if such registration includes an underwritten offering, dated the date
          of the closing under the underwriting agreement), signed by the
          independent public accountants who have certified the Company's
          financial statements included in such registration statement,

     covering substantially the same matters with respect to such registration
     statement (and the prospectus included therein) and, in the case of the
     accountants' letter, with respect to the events subsequent to the date of
     such financial statements, as are customarily covered in opinions of
     issuer's counsel and in accountants' letters delivered to the underwriters
     in underwritten public offerings of securities and, in the case of the
     accountants' letter, such other financial matters, and, in the case of the
     legal opinion, such other legal matters, as such seller or such holder or
     holders (or the underwriters, if any) may reasonably request;

          (vii)  notify each Holder of Option Securities covered by such
     registration statement, at any time when a prospectus relating thereto is
     required to be delivered under the Securities Act, upon 

                                       6
<PAGE>
 
     discovery that, or upon the happening of any event as a result of which,
     the prospectus included in such registration statement, as then in effect,
     includes an untrue statement of a material fact or omits to state any
     material fact required to be stated therein or necessary to make the
     statements therein not misleading in the light of the circumstances under
     which they were made, and at the request of any such seller or holder
     promptly prepare and furnish to such seller or holder a reasonable number
     of copies of a supplement to or an amendment of such prospectus as may be
     necessary so that, as thereafter delivered to the purchasers of such
     securities, such prospectus shall not include an untrue statement of a
     material fact or omit to state a material fact required to be stated
     therein or necessary to make the statement therein not misleading in the
     light of the circumstances under which they were made;

          (viii)  otherwise use its best efforts to comply with all applicable
     rules and regulations of the Commission, and make available to its security
     holders, as soon as reasonably practicable, a historical earnings statement
     covering the period of at least 12 months, but not more than 18 months,
     beginning with the first month of the first full fiscal quarter after the
     effective date of such registration statement, which earnings statement
     shall satisfy the provisions of Section 11(a) of the Securities Act, and
     will furnish to each such Holder at least five business days prior to the
     filing hereof a copy of any amendment or supplement to such registration
     statement or prospectus and shall not file any amendment or supplement to
     the registration statement to which any such Holder shall have reasonably
     objected on the grounds that such amendment or supplement does not comply
     in all material respects with the requirements of the Securities Act or the
     rules or regulations thereunder;

          (ix)  provide and cause to be maintained a transfer agent and
     registrar for all Option Securities covered by such registration statement
     from and after a date not later than the effective date of such
     registration statement; and

          (x)  uses its best efforts to list all Option Securities covered by
     such registration statement on any securities exchange on which any of the
     Common Stock is then listed or quoted on a recognized quotation service
     which also provides quotations of the Common Stock.

The Company may require each Holder of Option Securities covered by the
registration statement to furnish the Company such information regarding such
Holder and the distribution of such Option Securities as the Company may from
time to time reasonably request in writing.

     Each Holder of Option Securities agrees, as a condition of this Agreement,
that, upon receipt of any notice from the Company of the happening of any event
of the kind described in Section 8.3(vii) hereof, (i) such Holder will forthwith
discontinue such Holder's disposition of Option Securities pursuant to the
registration statement covering such Option Securities until such Holder's
receipt of the copies of the supplemented or amended prospectus contemplated by
Section 8.3(vii), (ii) such Holder will promptly deliver copies of such
supplemented or amended prospectus to each purchaser or potential purchaser to
whom such Holder had delivered the prospectus prior to such supplementation or
amendment, and (iii) if so directed by the Company, will deliver to the Company
(at the Company's expense) all copies, other than permanent file copies, then in
such Holder's possession of the prospectus relating to such Option Securities
current at the time of receipt of such notice.

     SECTION 8.4  Underwritten Offerings.  If the Company at any time proposes
to register any of its securities under the Securities Act, as contemplated by
Section 8 hereof, and such securities are to be 

                                       7
<PAGE>
 
distributed by or through one or more underwriters, the Company will, if
requested by any Holder of Option Securities as provided in Section 8.1 and
subject to the provisions of this Section 8.4, arrange for such underwriters to
include all of the Option Securities to be offered and sold by such holder among
the securities to be distributed by such underwriters. In the event that the
managing underwriter of any underwritten offering informs the Company and the
Holder or Holders of Option Securities requesting the inclusion of their
securities in such offering in writing of its belief that the number of
securities requested to be sold in such offering exceeds the number which can be
sold in such offering, then the Company will include in such offering only
securities proposed to be sold by Company for its own account and decrease the
number of Option Securities so proposed to be sold and requested to be included
in such offering (pro rata on the basis of the percentage of the securities, by
number of shares, of the Company requested to be included in the offering by the
Holder or Holders of such Option Securities and all other holders of the
Company's securities proposing to include shares in such offering) to the extent
necessary to reduce the number of securities to be included in such offering to
the level recommended by the managing underwriter. The holder or holders of
Option Securities to be distributed by such underwriters shall be parties to the
underwriting agreement between the Company and such underwriters and any
necessary or appropriate customary agreements, shall execute appropriate powers
of attorney, and may at their option, require that any or all of the
representations and warranties by, and the other agreements on the part of, the
Company to and for the benefit of such underwriters shall also be made to and
for the benefit of such Holder or Holders of Option Securities and that any or
all of the conditions precedent to the obligations of such underwriters under
such underwriting agreement be conditions precedent to the obligations of such
Holder or Holders of Option Securities. Any such Holder of Option Securities
shall not be required to make any representations or warranties to or agreement
with the Company or the underwriters other than representatives, warranties and
agreements regarding such Holder, such Holder's Option Securities and such
holder's intended method of distribution and any other representation required
by law.

     SECTION 8.5  Preparation; Reasonable Investigation.  In connection with the
preparation and filing of each registration statement under the Securities Act
covering Option Securities, the Company will give the Holder or Holders of
Option Securities registered under such registration statement, their
underwriters, if any, and their respective counsel and accountants, the
opportunity to participate in the preparation of such registration statement,
each prospectus included therein or filed with the Commission, and each
amendment or supplement thereto, and will give each of them such access to the
Company's books and records and such opportunities to discuss the business of
the Company with its offices and independent public accounts who have certified
its financial statements as shall be necessary, in the opinion of such Holders'
and such underwriters' respective counsel, to conduct a reasonable investigation
within the meaning of the Securities Act.

     SECTION 8.6  Indemnification.

     SECTION 8.6.1  Indemnification by the Company.  In the event of any
registration of any securities of the Company under the Securities Act, the
Company hereby agrees and will indemnify and hold harmless the Holder of any
Option Securities covered by such registration statement, it directors,
officers, representatives and agents, each other person who participates as an
underwriter in the offering or sale of such securities and each other person, if
any, who controls such Holder or any such underwriter within the meaning of the
Securities Act, against any losses, claims, damages or liabilities, joint or
several, to which such seller or any such director, officer, representative,
agent, underwriter or controlling person may become subject under the Securities
Act or otherwise, insofar as such losses, claims, damages or liabilities (or
actions or proceedings, whether commenced or threatened, in respect thereof)
arise out of or are based upon any untrue 

                                       8
<PAGE>
 
statement or alleged untrue statement of a material fact contained in any
registration statement under which such securities were registered under
Securities Act, any preliminary prospectus, final prospectus or summary
prospectus contained therein, or any amendment or supplement thereto, or any
omission or alleged omission to state therein a material fact required to be
stated therein or necessary to make the statements therein not misleading, and
the Company will indemnify such Holder and each such director, officer,
representative, agent, underwriter and controlling person for any legal or there
expenses reasonably incurred by them in connection with investigation or
defending any such loss, claim, liability, action or proceeding; provided,
however, that the Company shall not be liable in any such case to the extent
that such loss, claim, damage, liability (or action or proceeding in respect
thereof) or expense arises out of or is based upon an untrue statement or
alleged untrue statement or omission or alleged omission made in such
registration statement, any such preliminary prospectus, final prospectus,
summary prospectus, amendment or supplement in reliance upon and in conformity
with information furnished to the Company by such Holder specifically stating
that it is for use in the preparation thereof; and provided further, that the
Company shall not be liable to any person who participates as an underwriter in
the offering or sale of Option Securities or any person, if any, who controls
such underwriter within the meaning of the Securities Act, in any such case to
the extent that any such loss, claim, damage, liability (or action or proceeding
in respect thereof) or expense arises out of such person's failure to send or
give a copy of the final prospectus, as the same may be then supplemented or
amended, to the person asserting an untrue statement or alleged untrue statement
or omission or alleged omission at or prior to the written confirmation of the
sale of Option Securities to such person if such statement or mission was
contained in such final prospectus. Such indemnity shall remain in full force
and effect regardless of any investigation made by or on behalf of such seller
or any such director, officer, representative, agent, underwriter or controlling
person shall survive the transfer of such securities by such seller.

     SECTION 8.6.2  Indemnification by the Sellers.  The Company may require, as
a condition to including any Option Securities in any registration statement
filed pursuant to Section 8.3 hereof, that the Company shall have received an
undertaking reasonably satisfactory to it from the prospective seller of such
securities, to indemnify and hold harmless (in the same manner and to the same
extent as set forth in Section 8.6.1 hereof) the Company, each director,
officer, representative and agent of the Company and each other person, if any,
who controls the Company within the meaning of the Securities Act, with respect
to any statement or alleged statement in or omission or alleged omission from
such registration statement, any preliminary prospectus, final prospectus or
summary prospectus contained therein, or any amendment or supplement thereto, if
such statement or alleged statement or omission or alleged omission was made in
reliance upon and in conformity with information furnished to the Company by
such seller for use in the preparation of such registration statement,
preliminary prospectus, final prospectus, summary prospectus, amendment or
supplement.  Such indemnity shall remain in full force and effect, regardless of
any investigation made by or on behalf of the Company or any such director,
officer, representative, agent, or controlling person and shall survive the
transfer of such securities by such seller.

     SECTION 8.6.3  Notices of Claims and Procedure.  Promptly after receipt by
an indemnified person of notice of the commencement of any action or proceeding
involving a claim referred to in Section 8.6.1 or 8.6.2 hereof, such indemnified
person will, if a claim in respect thereof is to be made against an indemnified
party, give written notice to the latter of the commencement of such action;
provided, however, that the failure of any indemnified person to give notice as
provided herein shall not relieve the indemnifying party of its obligations
under Section 8.6.1 or 8.6.2 hereof, except to the extent that the indemnifying
party is actually prejudiced by such failure to give notice.  In case any such
action is brought against an indemnified person, unless in such indemnified
person's reasonable judgment a conflict of interest between such indemnified
person and such indemnifying party may exist in respect of such claim, the
indemnifying party shall be 

                                       9
<PAGE>
 
entitled to participate in and to assume the defense thereof jointly with any
other indemnifying party similarly notified to the extent that it may wish, with
counsel reasonably satisfactory to such indemnified person, and after notice
from the indemnifying party to such indemnified person of its election so to
assume the defense thereof, the indemnifying party shall not be liable to such
indemnified person for any legal or other expenses subsequently incurred by the
latter in connection with the defense thereof other than reasonable costs of
investigation. If, in such indemnified person's reasonable judgment a conflict
of interest does or may exist in respect of such claim, the indemnified person
or persons shall the right to select separate counsel to participate in the
defense of such action on behalf of such indemnified person or persons, in which
case the indemnifying party shall bear the costs of such defense. No
indemnifying party shall, without the consent of the indemnified person, consent
to the entry of any judgment or enter into any settlement which does not include
as an unconditional term thereof the giving by the claimant or plaintiff to such
indemnified person of a release from all liability with respect so such claim or
litigation and otherwise in form and substance satisfactory to the indemnified
person. The indemnifying party shall not be required to indemnify any
indemnified person against any settlement or judgment which is consented to by
an indemnified person without the consent of the indemnified party.

     SECTION 8.6.4  Other Indemnification.  Indemnification similar to that
specified in Sections 8.6.1, 8.6.2 and 8.6.3 hereof (with appropriate
modifications) shall be given by the Company and each Holder of Option
Securities covered by a registration statement with respect to any required
registration or other qualification of securities under federal or sate law or
regulation of any governmental authority other than the Securities Act.

     SECTION 8.6.5  Indemnification Payments.  The indemnification required by
this Section 8.6 shall be made by prompt payments of the amounts thereof during
the course of the investigation or defense, as and when bills are received or
expense, loss, damage or liability is incurred.

     SECTION 8.6.6  Contribution.  If any of the indemnification provisions
provided for in this Section 8.6 are determined to be unenforceable or
unavailable to an indemnified person in respect of any claim or action, then
each indemnifying party, in lieu of indemnifying such indemnified person, shall
contribute to the amount paid or payable by such indemnified person as a result
of such claims in such proportion as is appropriate to reflect not only the
relative benefits received by the indemnifying party and the indemnified person
from the registration statement, but also the relative fault of the indemnified
person and the indemnifying party in connection with the statements or omissions
which resulted in such claim or action as well as any other relevant equitable
considerations.  The relative fault of the indemnifying party and the
indemnified person shall be determined by reference to, among other things,
whether the untrue or alleged untrue statement of a material fact or the
omission or alleged omission to state a material fact relates to the information
supplied by the indemnifying party or by the indemnified person and their
relative intent, knowledge, access to information and opportunity to correct or
prevent such statement or omission.  The amount paid or payable by a party as a
result of the claims referred to above shall be deemed to include any legal or
other fees or expenses reasonably incurred by such Person in connection with
investigation or defending any action or claim.  No person guilty of fraudulent
misrepresentation (within the meaning of the Securities Act) shall be entitled
to contribution from any person that is not guilty of such fraudulent
misrepresentation.

     SECTION 8.7  Adjustments Affecting Option Securities.  The Company will not
effect or permit to occur any combination or subdivision of shares which would
materially adversely affect the ability of the 

                                       10
<PAGE>
 
holder of Option Securities to include such Option Securities in any
registration of its securities contemplated by this Section 8 or the
marketability of such Option Securities under any such registration.

     SECTION 9  Governing Law.  This Option shall be construed in accordance
with the laws of the State of Oklahoma applicable to contracts executed and to
be performed wholly within such state.

     SECTION 10  Notice.  Notices and other communications to be given to Holder
of this Option shall be delivered by hand or by first-class mail, postage
prepaid, to

                              Mr. Roger Lockhart
                              Post Office Box 10
                            Beaver, Arkansas 72613

(until another address is filed in writing by the Holder with the Company).
Notices or other communications to Company shall be deemed to have been
sufficiently given if delivered by hand or by first-class mail, postage prepaid
to Company at

                              The Vialink Company
                               13800 Benson Road
                          Edmond, Oklahoma 73013-6417
                        Attention:  Lewis B. Kilbourne

or such other address as the Company shall have designated by written notice to
such registered owner is herein provided.  Notice by mail shall be deemed given
when deposited in the United States mail, postage prepaid, as herein provided.

     SECTION 11.  Successors.  All the covenants and provisions of this
Agreement by or for the benefit of the Company shall bind and inure to the
benefit of its successors and assigns hereunder, and all covenants and
provisions of this Agreement by or for the benefit of the Holder of this
Agreement shall bind and inure to the benefit of the Holder of this Agreement.

     SECTION 12.  Termination.  This Agreement shall terminate as of the close
of business on the earlier of (i) December 31, 1996, in the event Company does
not complete the initial public offering of its common stock, (ii) the
Expiration Date, or (iii) such earlier date upon which the Options evidenced by
this Agreement shall have been exercised in full.  However, Section 8 and with
respect to the Holders representations set forth in Section 7, such Section and
representations shall continue on and after the Expiration Date if this Option
is fully or partially exercised on or before the Expiration Date.

     SECTION 13.  Benefits of this Agreement.  Nothing in this Agreement shall
be construed to give to any person or corporation other than the Company, and
its respective successors and assigns hereunder and the registered Holder of
this Agreement and the Option hereunder any legal or equitable right, remedy or
claim under this Agreement, but this Agreement shall be for the sole and
exclusive benefit of the Company and its respective successors and assigns
hereunder and the registered Holder of this Agreement and Option hereunder.

                                       11
<PAGE>
 
     IN WITNESS WHEREOF, Company has executed this Agreement on January 29,
1999.

                              THE VIALINK COMPANY


                              By:   /s/ Lewis B. Kilbourne
                                 -----------------------------------------------
                                    Lewis B. Kilbourne, CEO

                                       12
<PAGE>
 
                                 PURCHASE FORM
                  (TO BE EXECUTED BY THE HOLDER OF THE STOCK
                   OPTION IF EXERCISED IN WHOLE OR IN PART)

To:THE VIALINK COMPANY

     The undersigned (_________________________________________________________)
                     Please insert Social Security or other number of Subscriber
hereby irrevocably elects to exercise the right of purchase represented by the
Stock Option (the "Option") to which this Purchase Form is attached, for, and to
purchase thereunder, ___________________________________________________________
(________________) shares of Common Stock provided for therein and tenders
payment herewith to the order of THE VIALINK COMPANY in the amount of
$________________.  In accordance with Section 1 of the Option, the undersigned
requests that certificates for such shares of Common Stock be issued as follows:

Name:
     ---------------------------------------------------------------------------
Address:
        ------------------------------------------------------------------------
Deliver to:
           ---------------------------------------------------------------------
Address:
        ------------------------------------------------------------------------

and if said number of shares of Common Stock shall not be all the shares of
Common Stock purchasable thereunder, that a new Stock Option for the balance
remaining of shares of Common Stock purchasable under the Option be registered
in the name of, and delivered to the undersigned at the address stated below:

Name:
     ---------------------------------------------------------------------------
Address:
        ------------------------------------------------------------------------
Deliver to:
           ---------------------------------------------------------------------
Address:
        ------------------------------------------------------------------------

Dated:___________, _______    Signature

 
                              --------------------------------------------------
                              (Signature must conform in all respects to the
                              name of Holder as specified on the face of the
                              Stock Option in every particular, without
                              alteration, enlargement or any change whatever.)

                                       13
<PAGE>
 
                                ASSIGNMENT FORM
    (TO BE EXECUTED BY THE HOLDER OF THE STOCK OPTION ONLY UPON ASSIGNMENT)

FOR VALUE RECEIVED, the undersigned hereby sells, assigns and transfers unto
___________________________________________________________________ ("Assignee")
the right to purchase _______________________________________________(_________)
shares of Common Stock subject to purchase under the Stock Option (the "Option")
to which this Assignment is attached, and appoints _____________________________
Attorney to transfer said Option or portion thereof on the books of THE VIALINK
COMPANY with the full power of substitution in the premises. In accordance with
Section 3 of the Option, the undersigned requests that the Company execute,
issue and deliver a new Stock Option evidencing the rights of the Assignee to
purchase such assigned shares of Common Stock to Assignee as follows:

Name:
     ---------------------------------------------------------------------------
Address:
        ------------------------------------------------------------------------
Deliver to:
           ---------------------------------------------------------------------
Address:
        ------------------------------------------------------------------------

and if said number of shares of Common Stock shall not be all the shares of
Common Stock purchasable under the Option, that the Company execute, issue and
deliver a new Stock Option for the balance remaining of shares of Common Stock
purchasable under the Option to be registered in the name of, and delivered to
the undersigned at the address stated below:

Name:
     ---------------------------------------------------------------------------
Address:
        ------------------------------------------------------------------------
Deliver to:
           ---------------------------------------------------------------------
Address:
        ------------------------------------------------------------------------

Dated:___________, _______    

In the presence of:

                              Signature
Signature Guaranteed:

---------------------------   --------------------------------------------------
                              (Signature must conform in all respects to the
                              name of Holder as specified on the face of the
                              Stock Option in every particular, without
                              alteration, enlargement or any change whatsoever,
                              and the signature must be guaranteed in the usual
                              manner.)

                                       14