Document:

<PAGE>

                                                                EXHIBIT 10.14.17

                      EIGHTEENTH MODIFICATION AGREEMENT
                      ----------------------------------

     THIS AGREEMENT is made as of the 18th day of November, 1999, and is
effective as of September 1, 1999, by and among PNC BANK, NATIONAL ASSOCIATION,
successor by merger to Provident National Bank, a national banking association
with offices at 1600 Market Street, Philadelphia, Pennsylvania 19103 (the
"Bank"), and COMPANY (formerly SEI Corporation), a Pennsylvania corporation (the
"Borrower").

                                  BACKGROUND
                                  ----------

     Bank and Borrower have entered into a Credit Agreement effective as of May
31, 1992 as amended by a Waiver and First Modification Agreement between Bank
and Borrower dated as of September 30, 1992, a Second Modification Agreement
between Bank and Borrower dated as of April 19, 1993, a Third Modification
Agreement between Bank and Borrower dated as of May 31, 1993, a Fourth
Modification Agreement between Bank and Borrower dated as of March 14, 1994, a
Fifth Modification Agreement dated as of May 31, 1994, a Sixth Modification
Agreement dated as of May 5, 1995, a Seventh Modification Agreement effective as
of May 31, 1995, an Eighth Modification Agreement dated October 19, 1995, a
Ninth Modification Agreement dated March 31, 1996 a Tenth Modification Agreement
dated as of May 31, 1996, an Eleventh Modification Agreement dated October 1,
1996, a Release and Modification Agreement dated February 20, 1997, a Thirteenth
Modification Agreement dated May 30, 1997, a Fourteenth Modification Agreement
dated as of December 31, 1997, a Fifteenth Modification Agreement dated as of
March 31, 1998, a Sixteenth Modification Agreement dated as of May 29, 1998 and
a Seventeenth Modification Agreement dated as of February, 1999 (as so amended,
the "Credit Agreement") pursuant to which Bank agreed to make up to $50,000,000
in loans (the "Loans") to Borrower. Capitalized terms used herein and not
otherwise defined shall have the meanings ascribed to them in the Credit
Agreement. The Loans are evidenced by Borrower's note originally dated May 31,
1992 and amended and restated September 30, 1992, May 31, 1996 and October 1,
1996 (the "Note") in the principal amount of $50,000,000.

     The Borrower and Bank have agreed to extend the Termination Date, as
contemplated by the Credit Agreement, and to agree to certain other
modifications to the Credit Agreement, upon the terms and conditions set forth
herein.

     NOW, THEREFORE, the parties hereto, intending to be legally bound hereby,
agree as follows:

                                   AGREEMENT
                                   ---------

     1.   Terms.  Capitalized terms used herein and not otherwise defined herein
          -----
shall have the meanings given to such terms in the Credit Agreement.

     2.   Amendments to Credit Agreement.  The Credit Agreement is hereby
          ------------------------------
amended as follows:

               (a)  As contemplated by Section 9.15 of the Credit the
               Termination Date and the date on which the Credit Commitment
               shall expire and the Credit Period shall end is hereby extended
               to August 31, 2000.

               (b)  Section 2.2 of the Credit Agreement is hereby amended by
               changing the Commitment Fee rate from `1/10% per annum" to one-
               quarter of one percent (1/4%) per annum"

               (c)  Section 3.3(b) of the Credit Agreement is hereby amended to
               change the interest rate spread over the Eurodollar Rate from
               "three-tenths of one percent (.30%)" to "one and one-quarter
               percent (1.25%)".

                                                                              67

<PAGE>

               (d)  A new representation is hereby added to the Credit Agreement
               as Section 5.14, which shall read in full as follows:

                      "5.14. The Company has reviewed the areas within its
                      business and operations which could be adversely affected
                      by, and has developed or is developing a program to
                      address on a timely basis the risk that certain computer
                      applications used by the Company may be unable to
                      recognize and perform properly date-sensitive functions
                      involving dates prior to and after December 31, 1999 (the
                      "Year 2000 Problem"). The Year 2000 Problem will not
                      result, and is not reasonably expected to result, in any
                      material adverse effect on the business, properties,
                      assets, financial condition, results of operations or
                      prospects of the Company, or the ability of the Company to
                      duly and punctually pay or perform its obligations
                      hereunder and the other Loan Documents."

     3.   Loan Documents.  Except where the context clearly requires otherwise,
          --------------
all references to the Credit Agreement in the Note or any other document
delivered to Bank in connection therewith shall be to the Credit Agreement as
amended by this Agreement.

     4.   Borrower's Ratification. Borrower agrees that it has no defenses or
          -----------------------
set-offs against the Bank, its officers, directors, employees, agents or
attorneys with respect to the Note or the Credit Agreement, all of which are in
full force and effect and shall remain in full force and effect unless and until
modified or amended in writing in accordance with their terms. Borrower hereby
ratifies and confirms its obligations under the Note and the Credit Agreement
and agrees that the execution and the delivery of this Agreement does not in any
way diminish or invalidate any of its obligations thereunder.

     5.   Representations and Warranties.  Borrower hereby certifies that:
          ------------------------------

          (a)  except as otherwise previously disclosed to Bank in any manner
whatsoever, the representations and warranties made in the Credit Agreement are
true and correct as of the date hereof.

          (b)  no Event of Default under the Note or the Credit Agreement and no
event which with the passage of time or the giving of notice or both could
become an Event of Default, exists on the date hereof; and

          (c)  this Agreement has been duly authorized, executed and delivered
so as to constitute the legal, valid and binding obligation of Borrower,
enforceable in accordance with its terms.

     All of the above representations and warranties shall survive the making of
this Agreement.

     6.   No Waiver. This Agreement does not and shall not be deemed to
          ---------
constitute a waiver by Bank of any Event of Default under the Note or Credit
Agreement, or of any event which with the passage of time or the giving of
notice or both would constitute an Event of Default, nor does it obligate Bank
to agree to any further modifications of the terms of the Credit Agreement or
constitute a waiver of any of Bank's other rights or remedies.

     7.   Miscellaneous.
          -------------

          (a)  All terms, conditions, provisions and covenants in the Note, the
Credit Agreement, and all other documents delivered to Bank in connection
therewith shall remain unaltered and in full force and effect except as modified
or amended hereby. To the extent that any term or provision of this Agreement is
or may be deemed expressly inconsistent with any term or provision in the Credit
Agreement, the Note or any other document executed in connection therewith, the
terms and provisions hereof shall control.

          (b)  This Agreement shall be governed by and construed according to
the laws of the Commonwealth of Pennsylvania.

          (c)  This Agreement shall inure to the benefit of, and be binding
upon, the parties hereto and their respective successors and assigns and may be
executed in one or more counterparts, each of which shall be deemed an original,
but all of which together shall constitute one and the same instrument.

                                                                              68

<PAGE>

          IN WITNESS WHEREOF, the parties hereto have executed this Agreement as
of the day and year first above written.

                                               BORROWER
                                               --------

[SEAL]                                  SEI INVESTMENTS COMPANY
                                        (formerly SEI Corporation)

Attest:  /s/ Todd Cipperman             By:    /s/ Kathy Heilig
        ----------------------------           ------------------------------

Title:    Vice President                Title:  Controller and Treasurer
        ----------------------------           ------------------------------

                                               BANK
                                               ----

                                               PNC BANK, NATIONAL ASSOCIATION

                                        By:    /s/ Forrest B. Patterson, Jr.
                                               ------------------------------

                                        Title: Vice President
                                               ------------------------------

                                                                              69<PAGE>

                                                                EXHIBIT 10.14.18

                       NINETEENTH MODIFICATION AGREEMENT
                       ---------------------------------

     THIS AGREEMENT is made as of the 30th day of December, 1999, by and among
PNC BANK, NATIONAL ASSOCIATION, successor by merger to Provident National Bank,
a national banking association with offices at 1600 Market Street, Philadelphia,
Pennsylvania 19103 (the "Bank"), and SEI INVESTMENTS COMPANY (formerly SEI
Corporation), a Pennsylvania corporation (the "Borrower").

                                  BACKGROUND
                                  ----------

     Bank and Borrower have entered into a Credit Agreement effective as of May
31, 1992 as amended by a Waiver and First Modification Agreement between Bank
and Borrower dated as of September 30, 1992, a Second Modification Agreement
between Bank and Borrower dated as of April 19, 1993, a Third Modification
Agreement between Bank and Borrower dated as of May 31, 1993, a Fourth
Modification Agreement between Bank and Borrower dated as of March 14, 1994, a
Fifth Modification Agreement dated as of May 31, 1994, a Sixth Modification
Agreement dated as of May 5, 1995, a Seventh Modification Agreement effective as
of May 31, 1995, an Eighth Modification Agreement dated October 19, 1995, a
Ninth Modification Agreement dated March 31, 1996 a Tenth Modification Agreement
dated as of May 31, 1996, an Eleventh Modification Agreement dated October 1,
1996, a Release and Modification Agreement dated February 20, 1997, a Thirteenth
Modification Agreement dated May 30, 1997, a Fourteenth Modification Agreement
dated as of December 31, 1997, a Fifteenth Modification Agreement dated as of
March 31, 1998, a Sixteenth Modification Agreement dated as of May 29, 1998, a
Seventeenth Modification Agreement dated as of February, 1999 and an Eighteenth
Modification Agreement effective as of September 1, 1999 (as so amended, the
"Credit Agreement") pursuant to which Bank agreed to make up to $50,000,000 in
loans (the "Loans") to Borrower. Capitalized terms used herein and not otherwise
defined shall have the meanings ascribed to them in the Credit Agreement. The
Loans are evidenced by Borrower's note originally dated May 31, 1992 and amended
and restated September 30, 1992, May 31, 1996 and October 1, 1996 (the "Note")
in the principal amount of $50,000,000.

     The Borrower and Bank have agreed to extend the Termination Date, as
contemplated by the Credit Agreement, and to agree to certain other
modifications to the Credit Agreement, upon the terms and conditions set forth
herein.

     NOW, THEREFORE, the parties hereto, intending to be legally bound hereby,
agree as follows:

                                   AGREEMENT
                                   ---------

     1.   Terms.  Capitalized terms used herein and not otherwise defined herein
          -----
shall have the meanings given to such terms in the Credit Agreement.

     2.   Amendments to Credit  Agreement.  The Credit Agreement is hereby
          -------------------------------
amended by amending and restating Section 7.10(g) thereof to read in full as
follows:

                    "(g) Purchases by the Company of its common stock (to be
                    retired by the Company) of up to an aggregate consideration
                    of $350,000,000 (cumulatively since the institution of its
                    stock repurchase program), less the consideration paid by
                    the Company for the purchase of its common stock as of the
                    date hereof,"

     3.   Loan Documents.  Except where the context clearly requires otherwise,
          --------------
all references to the Credit Agreement in the Note or any other document
delivered to Bank in connection therewith shall be to the Credit Agreement as
amended by this Agreement.

     4.   Borrower's Ratification. Borrower agrees that it has no defenses or
          -----------------------
set-offs against the Bank, its officers, directors, employees, agents or
attorneys with respect to the Note or the Credit Agreement, all of which are in
full force and effect and shall remain in full force and effect unless and until
modified or amended in writing in accordance with their terms. Borrower hereby
ratifies and confirms its obligations under the Note and the Credit Agreement
and agrees that the execution and the delivery of this Agreement does not in any
way diminish or invalidate any of its obligations thereunder.

                                                                              71
<PAGE>

     5.   Representations and Warranties.  Borrower hereby certifies that:
          ------------------------------

          (a)  except as otherwise previously disclosed to Bank in any manner
whatsoever, the representations and warranties made in the Credit Agreement are
true and correct as of the date hereof.

          (b)  no Event of Default under the Note or the Credit Agreement and no
event which with the passage of time or the giving of notice or both could
become an Event of Default, exists on the date hereof; and

          (c)  this Agreement has been duly authorized, executed and delivered
so as to constitute the legal, valid and binding obligation of Borrower,
enforceable in accordance with its terms.

     All of the above representations and warranties shall survive the
making of this Agreement.

     6.   No Waiver. This Agreement does not and shall not be deemed to
          ---------
constitute a waiver by Bank of any Event of Default under the Note or Credit
Agreement, or of any event which with the passage of time or the giving of
notice or both would constitute an Event of Default, nor does it obligate Bank
to agree to any further modifications of the terms of the Credit Agreement or
constitute a waiver of any of Bank's other rights or remedies.

     7.   Miscellaneous.
          -------------

          (a)  All terms, conditions, provisions and covenants in the Note, the
Credit Agreement, and all other documents delivered to Bank in connection
therewith shall remain unaltered and in full force and effect except as modified
or amended hereby. To the extent that any term or provision of this Agreement is
or may be deemed expressly inconsistent with any term or provision in the Credit
Agreement, the Note or any other document executed in connection therewith, the
terms and provisions hereof shall control.

          (b)  This Agreement shall be governed by and construed according to
the laws of the Commonwealth of Pennsylvania.

          (c)  This Agreement shall inure to the benefit of, and be binding
upon, the parties hereto and their respective successors and assigns and may be
executed in one or more counterparts, each of which shall be deemed an original,
but all of which together shall constitute one and the same instrument.

     IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of
the day and year first above written.

                                                   BORROWER
                                                   --------

[SEAL]                                     SEI INVESTMENTS COMPANY
                                                   (formerly SEI Corporation)

Attest: /s/ Todd Cipperman                 By:     /s/ Kathy Heilig
        --------------------------                 -----------------------------

Title:  Vice President                     Title:  Controller and Treasurer
        --------------------------                 -----------------------------

                                                   BANK
                                                   ----

                                           PNC BANK, NATIONAL ASSOCIATION

                                           By:     /s/ Forrest B. Patterson, Jr.
                                                   -----------------------------

                                           Title:   Vice President
                                                   -----------------------------

                                                                              72

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00005-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00005-of-00352.parquet"}]]