Document:

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                                                                   EXHIBIT 10.11

                             Cantor Fitzgerald, L.P.
                          Cantor Fitzgerald Securities
                             One World Trade Center
                            New York, New York 10048

                                                     June 2, 2000

eSpeed, Inc.
One World Trade Center
New York, New York 10048

Dear Sirs:

         Reference is made to (i) the Subscription Agreement, dated April 26,
2000, by and among eSpeed, Inc. (the "Company"), Cantor Fitzgerald, L.P.
("Cantor") and Dynegy, Inc., (ii) the Subscription Agreement, dated April 26,
2000, by and among the Company, Cantor and The Williams Companies, Inc., and
(iii) the Stock Purchase Agreement, dated April 26, 2000 (the "Stock Purchase
Agreement"), by and between the Company and Cantor Fitzgerald Securities.

         In connection with Cantor's obligations under Section 12 of each of
these Subscription Agreements, the undersigned hereby request that you instruct
your transfer agent to convert an aggregate of 3,375,348 shares of Class B
Common Stock held by Cantor Fitzgerald Securities into the same number of shares
of Class A Common Stock. In addition, in connection with the transactions
contemplated by the Stock Purchase Agreement, the undersigned hereby agree that
the Initial Shares (as defined in the Stock Purchase Agreement) shall consist of
789,071 shares of Class A Common Stock and request that you instruct your
transfer agent to convert, prior to the Share Purchase Closing (as defined in
the Stock Purchase Agreement), 789,071 shares of Class B Common Stock held by
Cantor Fitzgerald Securities into the same number of shares of Class A Common
Stock (which shares shall then be sold at the Share Purchase Closing by Cantor
Fitzgerald Securities to you as contemplated by the Stock Purchase Agreement).

         By execution of this letter agreement, Cantor Fitzgerald Securities and
the Company are also agreeing that the Stock Purchase Agreement is hereby
amended to provide that the Initial Shares shall be shares of Class A Common
Stock rather than Class B Common Stock. Except as so amended, the Stock Purchase
Agreement shall remain in full force and effect.

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         If you are in agreement with the foregoing, please so indicate in the
space below provided for such purpose.

                                       CANTOR FITZGERALD, L.P.

                                       By: /s/ Howard W. Lutnick
                                           ----------------------
                                           Name: Howard W. Lutnick
                                           Title: Chairman

                                       CANTOR FITZGERALD SECURITIES

                                       By:  /s/ Howard W. Lutnick
                                           ----------------------
                                           Name: Howard W. Lutnick
                                           Title: President

AGREED:

ESPEED, INC.

By: /s/ Howard W. Lutnick
    -----------------------
    Name: Howard W. Lutnick
    Title: Chairman and Chief Executive Officer<PAGE>

NEITHER THIS WARRANT NOR THE SHARES OF CLASS A COMMON STOCK ISSUABLE UPON
EXERCISE OF THIS WARRANT HAVE BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933,
AND NEITHER THIS WARRANT NOR SUCH SHARES MAY BE SOLD, ENCUMBERED OR OTHERWISE
TRANSFERRED EXCEPT PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER SUCH
ACT OR AN EXEMPTION FROM SUCH REGISTRATION REQUIREMENT, AND, IF AN EXEMPTION
SHALL BE APPLICABLE, THE HOLDER SHALL HAVE DELIVERED AN OPINION OF COUNSEL
ACCEPTABLE TO THE COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED.

Void after 5:00 p.m. Eastern Standard Time, on June 5, 2010.

                    WARRANT TO PURCHASE CLASS A COMMON STOCK

                                       OF

                                  eSPEED, INC.

         FOR VALUE RECEIVED, eSPEED, INC. (the "Company"), a Delaware
corporation, hereby certifies that Dynegy Inc. (the "Initial Holder"), or its
permitted assigns (together with the Initial Holder, the "Holder"), is entitled
to purchase from the Company, at any time or from time to time commencing on the
Exercise Date set forth in Section 4 hereof (as the same may be accelerated
pursuant to Section 4(c) hereof) and prior to 5:00 P.M., Eastern Standard Time,
on June 5, 2010 a total of 666,666 fully paid and non-assessable shares of Class
A Common Stock, par value $.01 per share, of the Company for a purchase price of
$35.203125 per share. (Hereinafter, (i) said Class A Common Stock, together with
any other equity securities which may be issued by the Company with respect
thereto or in substitution therefor, is referred to as the "Class A Stock," (ii)
the shares of the Class A Stock purchasable hereunder are referred to as the
"Warrant Shares," (iii) the aggregate purchase price payable hereunder for the
Warrant Shares is referred to as the "Aggregate Warrant Price," (iv) the price
payable hereunder for each of the Warrant Shares is referred to as the "Per
Share Warrant Price," (v) this Warrant, and all warrants hereafter issued in
exchange or substitution for this Warrant are referred to as the "Warrant" and
(vi) the holder of this Warrant is referred to as the "Holder.") The number of
Warrant Shares and the securities (if applicable) for which this Warrant is
exercisable and the Per Share Warrant Price are subject to adjustment as
hereinafter provided under Section 3.

         1. Exercise of Warrant. This Warrant may be exercised, in whole at any
time or in part from time to time, commencing on the Exercise Date set forth in
Section 4 hereof (as the same may be accelerated pursuant to Section 4(c)
hereof) and prior to 5:00 P.M., Eastern Standard Time, on June 5, 2010 by the
Holder of this Warrant by the surrender of this Warrant (with the subscription
form at the end hereof duly executed) at the address set forth in Section 9(a)
hereof, together with proper payment of the Aggregate Warrant Price, or the
proportionate part thereof if this Warrant is exercised in part. The Aggregate
Warrant Price or Per Share Warrant Price shall be paid in cash, via wire
transfer to an account designated by the Company, or by certified or official
bank check payable to the order of the Company.

                                       -1-

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            If this Warrant is exercised in part, the Holder shall be entitled
to receive a new Warrant covering the number of Warrant Shares in respect of
which this Warrant has not been exercised and setting forth the proportionate
part of the Aggregate Warrant Price applicable to such Warrant Shares. Upon such
surrender of this Warrant, the Company will (a) issue a certificate or
certificates in the name of the Holder for the shares of the Class A Stock to
which the Holder shall be entitled, and (b) deliver the proportionate part
thereof if this Warrant is exercised in part, pursuant to the provisions of the
Warrant.

            No fractional shares shall be issued upon the exercise of this
Warrant. With respect to any fraction of a share called for upon any exercise
hereof, the Company shall pay to the Holder an amount in cash equal to such
fraction multiplied by the fair value of a share.

         2. Reservation of Warrant Shares. The Company agrees that, prior to the
expiration of this Warrant, the Company from and as of the date hereof, will
have authorized and in reserve, and will keep available, solely for issuance or
delivery upon the exercise of this Warrant, the shares of the Class A Stock as
from time to time shall be receivable upon the exercise of this Warrant.

         3. Adjustments for Corporate Events. The number and kind of securities
issuable upon the exercise of this Warrant, the Per Share Warrant Price and the
number of Warrant Shares for which this Warrant may be exercised shall be
subject to adjustment from time to time in accordance with the following
provisions:

                (a) Reorganization, Reclassification. In the event of a
reorganization, share exchange, or reclassification, other than a change in par
value, or from par value to no par value, or from no par value to par value or a
transaction described in subsection (b) or (c) below, this Warrant shall, after
such reorganization, share exchange or reclassification, be exercisable into the
kind and number of shares of stock or other securities or other property of the
Company which the holder of this Warrant would have been entitled to receive if
the holder had held the Warrant Shares issuable upon exercise of this Warrant
immediately prior to such reorganization, share exchange, or reclassification.

                (b) Merger, Consolidation or Sale of All or Substantially All
Assets. In the event of a merger or consolidation to which the Company is a
party or the sale of all or substantially all of the assets of the Company, this
Warrant shall, after such merger, consolidation or sale, be exercisable for the
kind and number of shares of stock and/or other securities, cash or other
property which the holder of this Warrant would have been entitled to receive if
the holder had held the Warrant Shares issuable upon exercise of this Warrant
immediately prior to such merger, consolidation or sale. Any such merger,
consolidation or sale shall require, as a condition thereto, that such other
party to such merger, consolidation or sale agree in writing to assume this
Warrant.

                (c) Subdivision or Combination of Shares. In case outstanding
shares of Class A Stock shall be subdivided, the Per Share Warrant Price shall
be proportionately reduced as of the effective date of such subdivision, or as
of the date a record is taken of the holders of

                                       -2-

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Class A Stock for the purpose of so subdividing, whichever is earlier. In case
outstanding shares of Class A Stock shall be combined, the Per Share Warrant
Price shall be proportionately increased as of the effective date of such
combination, or as of the date a record is taken of the holders of Class A Stock
for the purpose of so combining, whichever is earlier.

                (d) Stock Dividends. In case shares of Class A Stock are issued
as a dividend or other distribution on the Class A Stock (or such dividend is
declared), then the Per Share Warrant Price shall be adjusted, as of the date a
record is taken of the holders of Class A Stock for the purpose of receiving
such dividend or other distribution (or if no such record is taken, as at the
earliest of the date of such declaration, payment or other distribution), to
that price determined by multiplying the Per Share Warrant Price in effect
immediately prior to such declaration, payment or other distribution by a
fraction (i) the numerator of which shall be the number of shares of Class A
Stock outstanding immediately prior to the declaration or payment of such
dividend or other distribution, and (ii) the denominator of which shall be the
total number of shares of Class A Stock outstanding immediately after the
declaration or payment of such dividend or other distribution. In the event that
the Company shall declare or pay any dividend on the Class A Stock payable in
any right to acquire Class A Stock for no consideration, then, for purposes of
calculating such adjustment, the Company shall be deemed to have made a dividend
payable in Class A Stock in an amount of shares equal to the maximum number of
shares issuable upon exercise of such rights to acquire Class A Stock.

                (e) Adjustment of Aggregate Number of Warrant Shares Issuable.
Upon each adjustment of the Per Share Warrant Price under the provisions of this
Section 3, the aggregate number of Warrant Shares issuable upon exercise of this
Warrant shall be adjusted to an amount determined by multiplying the Warrant
Shares issuable prior to such adjustment by a fraction determined by dividing
(x) the Per Share Warrant Price in effect immediately prior to the event causing
such adjustment by (y) such adjusted Per Share Warrant Price.

                (f) Minimum Adjustment. No adjustment of the Per Share Warrant
Price shall be made if the amount of any such adjustment would be an amount less
than 1% of the Per Share Warrant Price then in effect, but any such amount shall
be carried forward and an adjustment in respect thereof shall be made at the
time of and together with any subsequent adjustment which, together with such
amount and any other amount or amounts so carried forward, shall aggregate an
increase or decrease of 1% or more.

                (g) Treasury Shares. The number of shares of Class A Stock at
any time outstanding shall not include any shares thereof then directly or
indirectly owned or held by or for the account of the Company.

                (h) Notices. If at any time, (x) the Company shall declare a
stock dividend (or any other distribution except for cash dividends) on its
Class A Stock; (y) there shall be any capital reorganization or reclassification
of the Class A Stock, or any consolidation or merger to which the Company is a
party, or any sale or transfer of all of substantially all of the assets of the
Company; or (z) there shall be a voluntary or involuntary dissolution,
liquidation or winding-up of the Company; then, in any one or more of such
cases, the Company shall give written notice

                                      -3-

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to the Holder, not less than 10 days before any record date or other date set
for definitive action, or of the date on which such reorganization,
reclassification, sale, consolidation, merger, dissolution, liquidation or
winding up shall take place, as the case may be. Such notice shall also set
forth such facts as shall indicate the effect of such action (to the extent such
effect may be known at the date of such notice) on the current Per Share Warrant
Price and the kind and amount of Class A Stock and other securities and property
deliverable upon exercise of this Warrant. Such notice shall also specify the
date (to the extent known) as of which the holders of the Class A Stock of
record shall be entitled to exchange their Class A Stock for securities or other
property deliverable upon such reorganization, reclassification, sale,
consolidation, merger, dissolution, liquidation or winding up, as the case may
be. In addition, whenever the aggregate number of Warrant Shares issuable upon
exercise of this Warrant and Per Share Warrant Price is adjusted as herein
provided, the Chief Financial Officer of the Company shall compute the
adjusted number of Warrant Shares and Per Share Warrant Price in accordance with
the foregoing provisions and shall prepare a written certificate setting forth
such adjusted number of Warrant Shares and Per Share Warrant Price, and such
written instrument shall promptly be delivered to the recordholder of this
Warrant.

         4. Exercisability.

                (a) Exercise Date. This Warrant shall be vested immediately and
shall be exercisable as to all Warrant Shares commencing December 5, 2005 (the
"Exercise  Date"),  subject to acceleration as set forth in subsection (c)
below.

                (b) Commitment to Invest in Four Qualified Verticals. The
Initial Holder has agreed to invest $2.5 million in each of four Qualified
Verticals (as defined below) pursuant to the terms of that certain Subscription
Agreement, dated as of April 26, 2000, by and between the Company and the
Initial Holder (the "Subscription Agreement"). Such investment is required to be
made during the 12-month period following the date hereof (the "12-Month
Period"; which period may be increased by not more than six months (the
"Black-Out Period") if a public offering by the Company is commenced during such
12-Month Period and disclosure constraints resulting from such public offering
dictate a delay as determined by the Company). Upon any such determination by
the Company, the Company shall so notify the Initial Holder in writing prior to
the commencement of any Black-Out Period, which notice shall specify the time
period by which the 12-Month Period shall be increased and the new last day of
the 12-Month Period. Such notice shall be binding on the parties. For purposes
of this agreement, a "Qualified Vertical" shall have the meaning ascribed to it
in Section 3(b) of the Subscription Agreement.

                (c) Acceleration of Exercisability.

                                      -4-

<PAGE>

                    (i) Satisfaction of Acceleration Condition. Upon each
         satisfaction of an Acceleration Condition (as defined below), this
         Warrant shall become exercisable as to 25% of the aggregate Warrant
         Shares (i.e., 166,666 shares of Class A Stock). An "Acceleration
         Condition" shall be deemed satisfied after the occurrence of each of
         the following: (1) the formation of a Qualified Vertical, (2) the
         consummation and funding of a $2.5 million investment in a Qualified
         Vertical by the Subscriber and each of the three additional industry
         market participants (two in the case of the Newco Qualified Vertical,
         as defined in Section 3 of the Subscription Agreement), and (3) the
         consummation of any market participant's first transaction on the
         exchange of said Qualified Vertical; provided that in any event the
         Acceleration Condition shall be deemed satisfied on the eight-week
         anniversary of the satisfaction of the conditions set forth in clauses
         (1) and (2) above.

                    (ii) Not Exercisable Prior to First Anniversary of Date of
         Issuance. Notwithstanding the provisions of subsection (c)(i) above,
         in no event will this Warrant, or any portion thereof, become
         exercisable prior to October 1, 2001. In the event that an Acceleration
         Condition is satisfied prior to such date, then the exercisability of
         this Warrant in connection with such satisfaction shall be deferred
         until October 1, 2001.

         5. Fully Paid Stock; Taxes. The Company agrees that the shares of the
Class A Stock represented by each and every certificate for Warrant Shares
delivered on the proper exercise of this Warrant shall, at the time of such
delivery, be validly issued and outstanding, fully paid and non-assessable, and
not subject to preemptive rights, and the Company will take all such actions as
may be necessary to assure that the par value or stated value, if any, per share
of the Class A Stock is at all times equal to or less than the then Per Share
Warrant Price. Subject to Section 6(c) hereof, the Company further covenants and
agrees that it will pay, when due and payable, any and all federal and state
stamp, original issue or similar taxes that may be payable in respect of the
issuance of any Warrant Shares or certificates therefor. The Holder covenants
and agrees that it shall pay, when due and payable, all of its federal, state
and local income or similar taxes that may be payable in respect of the issuance
of any Warrant Shares or certificates therefor, if any.

         6. Transfer

                (a) Securities Laws. Neither this Warrant nor the Warrant
Shares issuable upon the exercise hereof have been registered under the
Securities Act of 1933, as amended (the "Securities Act"), or under any state
securities laws and unless so registered may not be transferred, sold, pledged,
hypothecated or otherwise disposed of unless an exemption from such registration
is available. In the event the Holder desires to transfer this Warrant or any of
the Warrant Shares issued in accordance with the terms hereof, the Holder must
give the Company prior written notice of such proposed transfer including the
name and address of the proposed transferee, unless such transfer is a transfer
of the Warrant Shares pursuant to an effective Registration Statement. Such
transfer may be made only either (i) upon publication by the Securities and
Exchange Commission (the "Commission") of a ruling, interpretation, opinion or
"no action letter" based upon facts presented to said Commission, or (ii) upon
receipt by the

                                       -5-

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Company of an opinion of counsel acceptable to the Company to the effect that
the proposed transfer will not violate the provisions of the Securities Act, the
Securities Exchange Act of 1934, as amended (the "Exchange Act"), or the rules
and regulations promulgated under either such act, or to the effect that the
Warrant or Warrant Shares to be sold or transferred have been registered under
the Securities Act of 1933, as amended, and that there is in effect a current
prospectus meeting the requirements of Subsection 10(a) of the Securities Act,
which is being or will be delivered to the purchaser or transferee at or prior
to the time of delivery of the certificates evidencing the Warrant or Warrant
Shares to be sold or transferred.

                (b) Registration Rights. The Warrant Shares are the subject of
the Registration Rights Agreement attached to the Subscription Agreement as
Exhibit D.

                (c) Swap or Hedging Transactions. Subject to Section 3(c) of the
Subscription Agreement, without the prior written consent of the Company, the
Holder may not enter into any swap or other hedging transaction relating to the
Warrants or the Warrant Shares.

                (d) Transfer. Subject to Section 4(c), without the prior written
consent of the Company, neither this Warrant, nor any interest herein, may be
sold, assigned, transferred, pledged, encumbered or otherwise disposed of. Any
sale, assignment, transfer, pledge, encumbrance or other disposition of this
Warrant attempted contrary to the provisions of this Warrant, or any levy of
execution, attachment or other process attempted upon the Warrant, shall be null
and void and without effect. The provision of this Section 6(d) shall not be
applicable to the Warrant Shares. Without limitation of the foregoing,
Subscriber agrees that if it transfers its rights hereunder to a Subsidiary
pursuant to Section 16(k) of the Subscription Agreement, it shall not sell,
assign or transfer the stock of such Subsidiary during the 12-month lock-up.

                (e) Legend and Stop Transfer Orders. Unless the Warrant Shares
have been registered under the Securities Act or eligible for resale pursuant to
Rule 144(k) under the Securities Act, upon exercise of any part of the Warrant
and the issuance of any of the Warrant Shares, the Company shall instruct its
transfer agent to enter stop transfer orders with respect to such shares, and
all certificates representing Warrant Shares shall bear on the face thereof
substantially the following legend, insofar as is consistent with Delaware law:

                    "The shares of Class A Common Stock represented by
                    this certificate have not been registered under the
                    Securities Act of 1933, as amended, and may not be
                    sold, offered for sale, assigned, transferred or
                    otherwise disposed of unless registered pursuant to
                    the provisions of that Act or an opinion of counsel
                    to the Company is obtained stating that such
                    disposition is in compliance with an available
                    exemption from such registration."

                                       -6-

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         7. Loss, etc. of Warrant. Upon receipt of evidence satisfactory to the
Company of the loss, theft, destruction or mutilation of this Warrant, and of
indemnity reasonably satisfactory to the Company, if lost, stolen or destroyed,
and upon surrender and cancellation of this Warrant if mutilated, the Company
shall execute and deliver to the Holder a new Warrant of like date, tenor and
denomination.

         8. Warrant Holder Not Shareholder. Except as otherwise provided herein,
this Warrant does not confer upon the Holder any right to vote or to consent to
or receive notice as a shareholder of the Company, as such, in respect of any
matters whatsoever, or any other rights or liabilities as a shareholder, prior
to the exercise hereof.

         9. Communication. No notice or other communication under this Warrant
shall be effective unless the same is in writing and is mailed by first-class
mail, postage prepaid, addressed to:

                (a) the Company at One World Trade Center, 103rd Floor, New
York, New York 10048, Attention: General Counsel, or such other address as the
Company has designated in writing to the Holder, or

                (b) the Holder at 1000 Louisiana, Suite 5800, Houston, Texas
77002, Attention: General Counsel, or such other address as the Holder has
designated in writing to the Company.

         10. Headings. The headings of this Warrant have been inserted as a
matter of convenience and shall not affect the construction hereof.

         11. Applicable Law. This Warrant shall be governed by and construed in
accordance with the law of the State of New York without giving effect to the
principles of conflict of laws thereof.

                                       -7-

<PAGE>

         IN WITNESS WHEREOF, the Company has caused this Warrant to be signed by
a duly authorized officer as of this 5th day of June, 2000.

                                            eSPEED, INC.

                                            By: /s/ Howard W. Lutnick
                                               ---------------------------
                                                Name: Howard W. Lutnick
                                                Title: Chairman and
                                                       Chief Executive Officer

                                      -8-

<PAGE>

                                  SUBSCRIPTION

         The undersigned, __________________________________________, pursuant
to the provisions of the foregoing Warrant, hereby agrees to subscribe for the
purchase of _________________________ shares of the Class A Common Stock of
eSPEED, INC. covered by said Warrant, and makes payment therefor in full at the
price per share provided by said Warrant.

Dated                                      Signature
      ------------------                             ---------------------------
                                            Address
                                                    ----------------------------

                                   ASSIGNMENT

         FOR VALUE RECEIVED _________________________ hereby sells, assigns and
transfers unto _________________________ the foregoing Warrant and all rights
evidenced thereby, and does irrevocably constitute and appoint
_________________________, attorney, to transfer said Warrant on the books of
eSPEED, INC.

Dated                                      Signature
      ------------------                             ---------------------------
                                            Address
                                                    ----------------------------

                               PARTIAL ASSIGNMENT

         FOR VALUE RECEIVED _________________________ hereby assigns and
transfers unto _________________________ the right to purchase
_________________________ shares of the Class A Common Stock of eSPEED, INC. by
the foregoing Warrant, and a proportionate part of said Warrant and the rights
evidenced hereby, and does irrevocably constitute and appoint
_________________________, attorney, to transfer that part of said Warrant on
the books of eSPEED, INC.

Dated                                      Signature
      ------------------                             ---------------------------
                                            Address
                                                    ----------------------------

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