<PAGE>
                                                                   Exhibit 10.26


             JOINDER AND AMENDMENT TO SECURITIES PURCHASE AGREEMENT


         THIS JOINDER AND AMENDMENT TO SECURITIES PURCHASE AGREEMENT (this
"Joinder and Amendment Agreement") is made as of this 18th day of August, 2001
by and among Bentley Systems, Incorporated, a Delaware corporation (the
"Company"), Gabriel Norona, Francisco Norona, Richard D. Bowman, Andrew
Panayotoff, Orestes Norat and Robert Cormack (collectively, the "Purchasers"),
and for purposes of consenting to the amendment set forth herein, Gregory S.
Bentley, Keith A. Bentley, Barry J. Bentley, Cristobal Conde, David Ehret,
Robert Greifeld, Malcolm S. Walter and Argosy Investment Partners II, L.P. All
initially capitalized terms used but not otherwise defined in this Joinder and
Amendment Agreement shall have the meanings given to such terms in the
Securities Purchase Agreement (as such term is hereinafter defined).

                                   BACKGROUND

         1. On December 26, 2000, the Company entered into the Securities
Purchase Agreement (the "Securities Purchase Agreement") with the several
purchasers named in Schedule I attached thereto (the "Initial Purchasers") and
Raymond B. Bentley and Richard P. Bentley for certain limited purposes specified
therein, with respect to the Company's sale and the Initial Purchasers' purchase
of an aggregate 75,000 shares of the Senior Class C Common Stock of the Company
(the "Class C Shares") and Common Stock Purchase Warrants to purchase up to an
aggregate 1,040,000 shares of Class B Non-Voting Common Stock of the Company
("Class B Shares"). The aggregate price of the Class C Shares and warrants so
purchased and sold was $7.5 million.

         2. Pursuant to Section 1.2(c) of the Securities Purchase Agreement, the
Company had the right and option to sell up to an aggregate 75,000 additional
Class C Shares and Common Stock Purchase Warrants to purchase up to an aggregate
1,040,000 additional Class B Shares in one or more closings on or prior to June
30, 2001.

         3. On July 2, 2001 (a) the Securities Purchase Agreement was amended
("SPA Amendment No. 1") to extend the date for the closing of the sale of
additional Class C Shares and Common Stock Purchase Warrants to on or prior to
September 30, 2001 and (b) Argosy Investment Partners II, L.P. and Malcolm S.
Walter (the "Second Round Purchasers") joined in the Securities Purchase
Agreement in connection with their purchase of an aggregate 26,000 Class C
Shares and Common Stock Purchase Warrants to purchase up to an aggregate
360,533.3 Class B Shares. The aggregate price of the Class C Shares and warrants
so purchased and sold was $2.6 million.

         4. The Company and the Purchasers desire to sell and purchase,
respectively, an aggregate 35,000 Class C Shares and Common Stock Purchase
Warrants to purchase 485,333 Class B Shares on the date hereof. Such sale and
purchase shall be an Additional Closing under the Securities Purchase Agreement.
In order to effect such transaction, the Purchasers desire to join in the
Securities Purchase Agreement in accordance with Section 1.2(c) thereof.


                                      -1-
<PAGE>

         5. The Company also desires hereby to further amend the Securities
Purchase Agreement to re-define the stockholders who shall, pursuant to Section
6.6 of the Securities Purchase Agreement, be excluded from voting with respect
to certain cash compensation that may be paid by the Company to the Bentleys. In
accordance with Section 6.14 of the Securities Purchase Agreement, all parties
thereto must consent in writing to an amendment to such Section 6.6.

                  NOW THEREFORE, in consideration of the promises and the
agreements contained herein, the parties hereto, intending to be legally bound,
hereby agree as follows:

         1.1 Joinder. In connection with the purchase by him of the number of
Class C Shares and Common Stock Purchase Warrants to purchase the number of
Class B Shares indicated on Schedule I attached hereto, each of the Purchasers
hereby acknowledges and agrees that, effective as of the date hereof, he shall
be added as a party to the Securities Purchase Agreement, as amended by SPA
Amendment No. 1 and as further amended by this Joinder and Amendment Agreement,
and shall be bound by all provisions of the Securities Purchase Agreement, as so
amended, to the same extent as each of the Initial Purchasers and the Second
Round Purchasers, except for Section 6.1 relating to payment of the Purchasers'
expenses by the Company. The payment of the Purchasers' expenses shall instead
be governed by Section 10.2 of the Agreement and Plan of Merger, dated as of the
date hereof, among the Company, GP Acquisition Sub, Inc. and the Purchasers.

         1.2 Disclosure Statement. Pursuant to Section 1.2(c) of the Securities
Purchase Agreement, the Company has provided the Purchasers with a Disclosure
Statement dated the date hereof and attached hereto as Exhibit A, which
Disclosure Statement shall serve as the Disclosure Statement related to the
Additional Closing to which this Joinder and Amendment Agreement relates.

         1.3 Financial Statements. The Company has delivered to the Purchasers
its audited balance sheet as of December 31, 2000 and the related audited
consolidated statements of income and cash flow for the twelve months ended
December 31, 2000 and its unaudited balance sheet as of June 30, 2001 (the
"Balance Sheet") and the related unaudited consolidated statements of income and
cash flow for the six months ended June 30, 2001. All such financial statements
have been prepared in accordance with generally accepted accounting principles
applied on a consistent basis throughout the periods indicated ("GAAP") and
fairly present the financial condition and operating results of the Company as
of and for the periods set forth therein in accordance with GAAP, consistently
applied, except that the Balance Sheet may not contain all footnotes required by
GAAP, and is subject to normal recurring year end adjustments. Except as set
forth in the Balance Sheet and the related notes thereto, the Company has no
material liabilities, contingent or otherwise, other than (a) current
liabilities (as defined by GAAP) incurred in the ordinary course of business
subsequent to June 30, 2001 and (b) obligations under contracts and commitments
incurred in the ordinary course of business that are not required: (i) under
GAAP to be reflected on the Balance Sheet, or (ii) to be disclosed pursuant to
Statement of Financial Accounting Standards No.5.


                                      -2-
<PAGE>

         1.4 Amendment.

                  (a) Section 6.6 of the Securities Purchase Agreement is hereby
amended by deleting "Bentleys" from each of the parenthetical clauses in such
Section 6.6 and replacing that term with "Insiders," so that each such
parenthetical clause reads as follows:

         "(which holders shall, for the purposes of such vote, not include the
         Insiders or holders controlled by the Insiders) . . ."

                  (b) Section 6.6 is hereby amended by adding the following as
the final sentence of such Section:

         "For purposes hereof, `Insiders' means the Bentleys together with (i)
         any persons who are employees of the Company or any of its subsidiaries
         on the date such person first acquires shares of Stock, (ii) any
         persons who acquire shares of Stock within thirty (30) days of becoming
         employees of the Company or any of its subsidiaries, and (iii) the
         immediate family members of any persons referred to in subclauses (i)
         or (ii)."

                  (c) Except as specifically amended hereby, all of the terms
and conditions of the Securities Purchase Agreement, as previously amended by
SPA Amendment No. 1, shall remain in full force and effect. All references to
the Securities Purchase Agreement in any other document or instrument shall be
deemed to mean such Securities Purchase Agreement as amended by SPA Amendment
No. 1 and this amendment. The parties hereto agree to be bound by the terms and
obligations of the Securities Purchase Agreement, as amended by SPA Amendment
No. 1 and this amendment, as though the terms and obligations of the Securities
Purchase Agreement were set forth herein.

         1.5 Counterparts. This Joinder and Amendment Agreement may be executed
in any number of counterparts, all of which taken together shall constitute one
and the same instrument, and any of the parties hereto may execute this Joinder
and Amendment Agreement by signing any such counterpart.

                            [signature page follows]


                                      -3-
<PAGE>
         IN WITNESS WHEREOF, the parties hereto, intending to be legally bound,
have caused this Joinder and Amendment Agreement to be executed as of the date
first above written.

                                    COMPANY:


                                    BENTLEY SYSTEMS, INCORPORATED


                                    By:      /s/ David G. Nation
                                       -----------------------------------------
                                       Name:    David G. Nation
                                       Title:   Senior Vice President

                                    PURCHASERS:


                                             /s/ Gabriel Norona
                                    --------------------------------------------
                                    Gabriel Norona


                                             /s/ Francisco Norona
                                    --------------------------------------------
                                    Francisco Norona


                                             /s/ Richard D. Bowman
                                    --------------------------------------------
                                    Richard D. Bowman


                                             /s/ Andrew Panayotoff
                                    --------------------------------------------
                                    Andrew Panayotoff


                                             /s/ Orestes Norat
                                    --------------------------------------------
                                    Orestes Norat


                                             /s/ Robert Cormack
                                    --------------------------------------------
                                    Robert Cormack


               [Signature Page 1 of 2 to Joinder and Amendment to
                         Securities Purchase Agreement]


                                      -4-
<PAGE>

         The undersigned, in accordance with Section 6.14 of the Securities
Purchase Agreement, hereby consent to the amendment to Section 6.6 of the
Securities Purchase Agreement set forth in this Joinder and Amendment Agreement
as of the date first above written.


                                   /s/ Gregory S. Bentley
                          --------------------------------------------
                          Gregory S. Bentley


                                   /s/ Keith A. Bentley
                          --------------------------------------------
                          Keith A. Bentley



                                   /s/ Barry J. Bentley
                          --------------------------------------------
                          Barry J. Bentley



                                   /s/ Cristobal Conde
                          --------------------------------------------
                          Cristobal Conde



                          --------------------------------------------
                          Robert Greifeld



                                   /s/ David Ehret
                          --------------------------------------------
                          David Ehret



                                   /s/ Malcolm S. Walter
                          --------------------------------------------
                          Malcolm S. Walter


                          ARGOSY INVESTMENT PARTNERS II, L.P.
                          By:  Argosy Associates II, L.P., its General Partner
                          By:  Argosy Associates II, Inc., its General Partner

                               By:    /s/ Kirk B. Griswold
                                   --------------------------------------------
                                   Name:  Kirk B. Griswold, Vice President

               [Signature Page 2 of 2 to Joinder and Amendment to
                         Securities Purchase Agreement]


                                      -5-
<PAGE>

                                   SCHEDULE I
                              TO JOINDER AGREEMENT


<TABLE>
<CAPTION>
                                                        Warrants to Purchase
                              Shares of Senior Class    Shares of Class B Non-
Purchaser                     C Common Stock            Voting Common Stock
<S>                           <C>                       <C>
Gabriel Norona                20,574                    285,293
Francisco Norona               3,835                     53,176
Richard D. Bowman              3,475                     48,181
Andrew Panayotoff              2,770                     38,416
Orestes Norat                  2,770                     38,416
Robert Cormack                 1,576                     21,851
</TABLE>


                                      -6-

<PAGE>

                                    EXHIBIT A
                              DISCLOSURE STATEMENT


                                      -7-
<PAGE>



                    JOINDER TO SECURITIES PURCHASE AGREEMENT


         THIS JOINDER TO SECURITIES PURCHASE AGREEMENT (this "Joinder
Agreement") is made as of this 18th day of September, 2001 by and among Bentley
Systems, Incorporated, a Delaware corporation (the "Company"), Gabriel Norona
and Francisco Norona (collectively, the "Purchasers"). All initially capitalized
terms used but not otherwise defined in this Joinder Agreement shall have the
meanings given to such terms in the Securities Purchase Agreement (as such term
is hereinafter defined).

                                   BACKGROUND

         1. On December 26, 2000, the Company entered into the Securities
Purchase Agreement (the "Securities Purchase Agreement") with the several
purchasers named in Schedule I attached thereto (the "Initial Purchasers") and
Raymond B. Bentley and Richard P. Bentley for certain limited purposes specified
therein, with respect to the Company's sale and the Initial Purchasers' purchase
of an aggregate 75,000 shares of the Senior Class C Common Stock of the Company
(the "Class C Shares") and Common Stock Purchase Warrants to purchase up to an
aggregate 1,040,000 shares of Class B Non-Voting Common Stock of the Company
("Class B Shares"). The aggregate price of the Class C Shares and warrants so
purchased and sold was $7.5 million.

         2. Pursuant to Section 1.2(c) of the Securities Purchase Agreement, the
Company had the right and option to sell up to an aggregate 75,000 additional
Class C Shares and Common Stock Purchase Warrants to purchase up to an aggregate
1,040,000 additional Class B Shares in one or more closings on or prior to June
30, 2001.

         3. On July 2, 2001 (a) the Securities Purchase Agreement was amended to
extend the date for the closing of the sale of additional Class C Shares and
Common Stock Purchase Warrants to on or prior to September 30, 2001 and (b)
Argosy Investment Partners II, L.P. and Malcolm S. Walter (the "Second Round
Purchasers") joined in the Securities Purchase Agreement in connection with
their purchase of an aggregate 26,000 Class C Shares and Common Stock Purchase
Warrants to purchase up to an aggregate 360,533.3 Class B Shares. The aggregate
price of the Class C Shares and warrants so purchased and sold was $2.6 million.

         4. On the date hereof (a) the Company is acquiring Geopak Corporation,
a Florida corporation ("Geopak"), through the merger of Geopak into a wholly
owned subsidiary of the Company (the "Merger"), (b) in partial consideration of
the Merger, the Company is issuing an aggregate 35,000 Class C Shares to the
stockholders of Geopak (the "Stockholders") including the Purchasers, and (c)
the Stockholders and the Company are entering into a Joinder and Amendment to
Securities Purchase Agreement with respect to such purchase and sale of the
35,000 Class C Shares.

         5. The Company and the Purchasers desire to sell and purchase,
respectively, an additional aggregate 5,000 Class C Shares on the date hereof.
Such sale and purchase shall be an


                                      -1-
<PAGE>

Additional Closing under the Securities Purchase Agreement. In order to effect
such transaction, the Purchasers desire to join in the Securities Purchase
Agreement in accordance with Section 1.2(c) thereof.

                  NOW THEREFORE, in consideration of the promises and the
agreements contained herein, the parties hereto, intending to be legally bound,
hereby agree as follows:

         1.1 Joinder. In connection with the purchase by him of the number of
Class C Shares indicated on Schedule I attached hereto, each of the Purchasers
hereby acknowledges and agrees that, effective as of the date hereof, he shall
be added as a party to the Securities Purchase Agreement, as amended through the
date hereof, and shall be bound by all provisions of the Securities Purchase
Agreement, as so amended, to the same extent as each of the Initial Purchasers,
the Second Round Purchasers and the Stockholders, except for Section 6.1
relating to payment of the Purchasers' expenses by the Company. The payment of
the Purchasers' expenses shall instead be governed by Section 10.2 of the
Agreement and Plan of Merger, dated as of the date hereof, among the Company, GP
Acquisition Sub, Inc. and the Stockholders.

         1.2 Disclosure Statement. Pursuant to Section 1.2(c) of the Securities
Purchase Agreement, the Company has provided the Purchasers with a Disclosure
Statement dated the date hereof and attached hereto as Exhibit A, which
Disclosure Statement shall serve as the Disclosure Statement related to the
Additional Closing to which this Joinder Agreement relates.

         1.3 Financial Statements. The Company has delivered to the Purchasers
its audited balance sheet as of December 31, 2000 and the related audited
consolidated statements of income and cash flow for the twelve months ended
December 31, 2000 and its unaudited balance sheet as of June 30, 2001 (the
"Balance Sheet") and the related unaudited consolidated statements of income and
cash flow for the six months ended June 30, 2001. All such financial statements
have been prepared in accordance with generally accepted accounting principles
applied on a consistent basis throughout the periods indicated ("GAAP") and
fairly present the financial condition and operating results of the Company as
of and for the periods set forth therein in accordance with GAAP, consistently
applied, except that the Balance Sheet may not contain all footnotes required by
GAAP, and is subject to normal recurring year end adjustments. Except as set
forth in the Balance Sheet and the related notes thereto, the Company has no
material liabilities, contingent or otherwise, other than (a) current
liabilities (as defined by GAAP) incurred in the ordinary course of business
subsequent to June 30, 2001 and (b) obligations under contracts and commitments
incurred in the ordinary course of business that are not required: (i) under
GAAP to be reflected on the Balance Sheet, or (ii) to be disclosed pursuant to
Statement of Financial Accounting Standards No.5.

         1.4 Counterparts. This Joinder Agreement may be executed in any number
of counterparts, all of which taken together shall constitute one and the same
instrument, and any of the parties hereto may execute this Joinder Agreement by
signing any such counterpart.


                                      -2-
<PAGE>


         IN WITNESS WHEREOF, the parties hereto, intending to be legally bound,
have caused this Joinder Agreement to be executed as of the date first above
written.

                                  COMPANY:


                                  BENTLEY SYSTEMS, INCORPORATED


                                  By:      /s/ David G. Nation
                                     -----------------------------------------
                                        Name:  David G. Nation
                                        Title:    Senior Vice President
                                  PURCHASERS:


                                           /s/ Gabriel Norona
                                  --------------------------------------------
                                  Gabriel Norona


                                          /s/ Francisco Norona
                                  --------------------------------------------
                                  Francisco Norona

       [Signature Page 1 of 1 to Joinder to Securities Purchase Agreement]


                                      -3-
<PAGE>

                                   SCHEDULE I
                              TO JOINDER AGREEMENT

<TABLE>
<CAPTION>
                              Shares of Senior Class
Purchaser                     C Common Stock            Purchase Price
<S>                           <C>                       <C>
Gabriel Norona                2,500                     $250,000
Francisco Norona              2,500                     $250,000
</TABLE>


                                      -4-