Document:

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                                                                   Exhibit 10.23

                       FIRST AMENDMENT OF CREDIT AGREEMENT

     THIS FIRST AMENDMENT OF CREDIT AGREEMENT (this "Amendment") is entered into
to be effective as of November 28, 2000, between PRENTISS PROPERTIES ACQUISITION
PARTNERS, L.P., a Delaware limited partnership ("Borrower"), each of the lenders
which is a signatory to this Amendment (individually, a "Lender" and
collectively, "Lenders"), and BANK ONE, TEXAS, N.A., a national banking
association, as Administrative Agent (in such capacity, together with its
successors and assigns, "Administrative Agent").

                                 R E C I T A L S
                                 - - - - - - - -

     A. Reference is hereby made to that certain Credit Agreement dated as of
September 30, 1999, executed by Borrower, Lenders, Administrative Agent, and the
Co-Documentation Agents defined therein (as renewed, extended, modified, and
amended from time to time, the "Credit Agreement"), providing for a term loan
facility.

     B. Capitalized terms used herein shall, unless otherwise indicated, have
the respective meanings set forth in the Credit Agreement.

     C. The parties hereto desire to modify certain provisions contained in the
Credit Agreement, subject to the terms and conditions set forth herein.

     NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto agree as
follows:

     1. Amendments to the Credit Agreement.

     (a) Section 1.1 is hereby amended to delete the definitions of "Affiliate,"
"Aggregate EBITDA," "Approved Costs," "Distribution," "EBITDA,"
"EBITDA Adjustments," "Equity Issuance," "Existing Line of Credit," "Fixed
Charges," "Funds from Operations," "Indebtedness," "Liabilities," "Permitted
Distributions," "Permitted Recourse Debt," "Permitted Redemptions," "Recourse
Debt," and "Total Assets" in their entirety and replace such definitions with
the following:

          "Affiliate" of a Person means any other individual or entity who
     directly or indirectly controls, or is controlled by, or is under common
     control with, that Person. For purposes of this definition "control,"
     "controlled by," and "under common control with" mean possession, directly
     or indirectly, of power to direct (or cause the direction of) management or
     policies (whether through ownership of Stock, by contract, or otherwise).

          "Aggregate EBITDA" means, for the Companies for any period, (a) EBITDA
     of the Companies, minus (b) the Companies' Share of recognized net income
     of Unconsolidated Affiliates, plus (c) the Companies' Share of EBITDA of
     Unconsolidated Affiliates (other than Broadmoor), to the extent a Company
     is entitled to such amounts under the Constituent Documents of the
     applicable Unconsolidated Affiliate.

          "Approved Costs" means, for any Property, the sum of the acquisition,
     construction, and other capitalized costs of such Property (or the Stock of
     the Company that owns such Property), whether in the form of cash,
     property, liabilities assumed, or other consideration.

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          "Distribution" means, with respect to any Stock issued by a Person,
     (a) the declaration or payment of any dividend or distribution on or with
     respect to such Stock by such Person, (b) any loan or advance by that
     Person to, or other investment by that Person in, the holder of any of such
     Stock, and (c) any other payment by that Person with respect to such Stock
     (other than a Redemption).

          "EBITDA" means, for any Person or any Property for any period, the sum
     of (a) Net Income, plus (b) depreciation and amortization expense, plus (c)
     Interest Expense, plus (d) income taxes deducted from Net Income in
     accordance with GAAP, plus (e) extraordinary losses (and any unusual losses
     arising in or outside the ordinary course of business of such Person not
     included in extraordinary losses) determined in accordance with GAAP that
     have been reflected in the determination of Net Income, minus (f)
     extraordinary gains (and any unusual gains arising in or outside the
     ordinary course of business of such Person not included in extraordinary
     gains) determined in accordance with GAAP that have been reflected in the
     determination of Net Income, minus (g) earnings of Consolidated Affiliates
     for such period distributed to minority interests not previously deducted
     in the calculation of Net Income.

          "EBITDA Adjustments" means, for any Property for any period,
     appropriate accruals for items such as taxes, insurance, or other expenses
     determined by Borrower (subject to the reasonable approval of
     Administrative Agent), a management fee equal to the greater of actual fees
     incurred or two percent (2%) of in place actual rents, and a reserve of $1
     per square foot per year for office Properties and $0.25 per square foot
     for industrial Properties, all as determined in accordance with accounting
     principles reasonably acceptable to Administrative Agent, consistently
     applied.

          "Equity Issuance" means the issuance or sale by any Company of any
     Stock, or options, warrants, or other rights to subscribe for or otherwise
     acquire Stock, of such Company, other than the issuance by Borrower of
     Stock in Borrower to sellers of properties or non-cash assets as a partial
     payment of the purchase price of such assets.

          "Existing Line of Credit" means (a) that certain Credit Agreement
     dated May 23, 2000, executed by Borrower, Bank One, NA, as Administrative
     Agent, Bank of America, N.A., as Syndication Agent, Dresdner Bank AG, New
     York Branch and Grand Cayman Branch, as Documentation Agent, and the
     Lenders defined therein, as such Credit Agreement has been or may be
     modified, amended, renewed, extended, or restated from time to time, and
     (b) a revolving credit facility that replaces the facility described in
     clause (a) so long as Lenders hereunder constituting at least the Required
     Lenders are also lenders under such replacement revolving credit facility.

          "Fixed Charges" means, for the Companies on a consolidated basis for
     any period, the sum of (a) Debt Service during such period, and (b) all
     Distributions paid or payable during such period in respect of any
     preferred Stock of the Companies (including the Companies' Share of such
     Distributions in respect of any preferred Stock of their Unconsolidated
     Affiliates (other than Broadmoor)).

          "Funds from Operations" means, for any Person for any period, the sum
     of (a) Net Income plus depreciation and amortization expense (exclusive of
     amortization of financing costs), all as determined in accordance with
     GAAP, and (b) such Person's Share of Funds from Operations of any
     Unconsolidated Affiliates of such Person (calculated in accordance with
     clause (a) preceding); provided that there shall not be included in such
     calculation (i) any proceeds of any insurance policy

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     other than rental or business interruption insurance received by such
     Person, (ii) any gain or loss which is classified as "extraordinary" in
     accordance with GAAP, or (iii) any capital gains and taxes on capital
     gains. Funds from Operations shall not be reduced by any Distribution in
     respect of any preferred Stock of such Person.

          "Indebtedness" means, for any Person, all Liabilities of such Person,
     excluding (a) accounts payable and accrued expenses in each case incurred
     in the ordinary course of business and the payment of which is not past-due
     (unless payment is being contested in good faith by appropriate proceedings
     diligently conducted and for which reserves in accordance with GAAP or
     otherwise reasonably acceptable to Administrative Agent have been
     provided), and (b) Liabilities in which such Person maintains restricted
     cash deposits that are not included in Total Assets to satisfy payment
     thereof, but only to the extent of such cash deposits.

          "Liabilities" means (without duplication), for any Person, (a) any
     indebtedness, liabilities, or obligations required by GAAP to be classified
     upon such Person's balance sheet as liabilities, (b) any liabilities
     secured (or for which the holder of the Liability has an existing Right,
     contingent or otherwise, to be so secured) by any Lien existing on property
     owned or acquired by that Person, (c) any obligations that have been (or
     under GAAP should be) capitalized for financial reporting purposes,
     including all Capital Leases, (d) mandatory net obligations to purchase or
     repurchase such Person's Stock as calculated by Borrower in a manner
     reasonably acceptable to Administrative Agent, (e) Unfunded Liabilities,
     and (f) such Person's Share of any Liabilities of Unconsolidated Affiliates
     (other than of Broadmoor), and "Liability" means any of the Liabilities.

          "Permitted Distributions" means, for (a) Borrower for any fiscal year
     of Borrower, an amount of Distributions not to exceed ninety-five percent
     (95%) of Borrower's Funds from Operations for such fiscal year, and (b) PPT
     for any fiscal year of PPT, an amount of Distributions not to exceed
     ninety-five percent (95%) of PPT's Funds from Operations for such fiscal
     year.

          "Permitted Recourse Debt" means (a) Recourse Debt under the Existing
     Line of Credit not to exceed $300,000,000 at any time outstanding, and (b)
     other Recourse Debt (including the Obligation) not to exceed $400,000,000
     in the aggregate at any time outstanding.

          "Permitted Redemptions" means the Redemption by PPT and Borrower of
     Stock issued by PPT or Borrower not to exceed $150,000,000 in the aggregate
     during the term of this Agreement, provided that no Default exists or would
     result from such Redemption.

          "Recourse Debt" means, for any Person, Indebtedness of such Person
     that is not Non-Recourse Debt; provided that (a) Recourse Debt of the
     Companies shall include any Indebtedness guaranteed (other than Customary
     Recourse Exceptions) by PPT or Borrower, and (b) Recourse Debt of the
     Companies, as of any date, shall not include Indebtedness of any Excluded
     Companies so long as no Obligor is obligated (as guarantor or otherwise
     other than for Customary Recourse Exceptions) on such Indebtedness. To the
     extent that any Person has partial recourse obligations with respect to any
     Indebtedness, then only that portion of such Indebtedness that is not
     Non-Recourse Debt shall be considered to be Recourse Debt (e.g., if any
     such Person is personally liable for only $25,000,000 of Indebtedness equal
     to $100,000,000, then only $25,000,000 of such Indebtedness shall be
     Recourse Debt).

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          "Total Assets" means, as of any determination date, the sum of the
     following (without duplication):

          (a) the EBITDA Value of each Property owned by a Company for, and in
     which construction was completed and a certificate of occupancy was issued,
     more than twelve (12) months as of such determination date; plus

          (b) the EBITDA Value of each Property owned by a Company for, and in
     which construction was completed by a Company and a certificate of
     occupancy was issued, less than twelve (12) months as of such determination
     date and that has an Occupancy Rate of at least eighty-five percent (85%)
     for three (3) consecutive months; plus

          (c) so long as 123 North Wacker Drive is owned by a Company, then the
     Approved Costs of such Property until December 31, 2002 and, thereafter,
     the EBITDA Value of such Property; plus

          (d) the Approved Costs of each Property not included in (a) through
     (c) above; plus

          (e) the lesser of (i) $40,000,000, and (ii) the product of (A) seven
     (7), and (B) EBITDA for the four (4) fiscal quarters ending on such
     determination date in respect of management contracts between a Company and
     a third party (other than another Company); plus

          (f) the sum of (without duplication) Borrower's Share of the Approved
     Costs of each Property owned by an Unconsolidated Affiliate (other than
     Broadmoor) as of such determination date; plus

          (g) the Companies' cash and Cash Equivalents, in each case that are
     not subject to any Lien; plus

          (h) the lesser of (i) the Approved Costs of each other Property
     consisting of raw land, and (ii) two and one-half percent (2.5%) of Total
     Assets as of such date; plus

          (i) the Applicable Amount of each Contract Property to the extent that
     the calculation of Liabilities or Indebtedness includes any Unfunded
     Liabilities with respect to such Contract Property; plus

          (j) the Applicable Amount of each Development Property to the extent
     that the calculation of Liabilities or Indebtedness includes any Unfunded
     Liabilities with respect to such Development Property.

     If any Company that owns any Total Assets described above has any minority
     interests, then Total Assets shall be adjusted to exclude the minority
     interests' Share of such Total Assets. No Property can have a value,
     calculated as provided above, of less than $0.00.

     (b) Section 1.1 is hereby amended to add the following definitions:

          "Applicable Amount" means (a) with respect to a Contract Property, the
     lesser of (i) the purchase price of such Contract Property (or the Stock of
     the Person that owns such Contract

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     Property), and (ii) the maximum personal liability of the Companies to pay
     such purchase price as determined by Borrower in a manner reasonably
     acceptable to Administrative Agent, and (b) with respect to a Development
     Property, the unpaid balance of any Liabilities incurred to finance the
     costs of constructing or developing such Development Property to the extent
     that a Company is obligated (as guarantor or otherwise) with respect to
     such Liabilities.

          "Binding Agreement" means a binding agreement pursuant to which a
     Company has agreed to purchase a Contract Property or a Development
     Property from another Person and in which such Person may enforce rights
     and remedies at law or in equity against a Company for failure to purchase
     such Contract Property or Development Property and which remedies are not
     limited to retaining earnest money, escrow, liquidated damages not to
     exceed ten percent (10%) of the applicable purchase price, or other
     deposits of a Company or similar limitations on the liability of any
     Company.

          "Broadmoor" means Broadmoor Austin Associates, a Texas joint venture.

          "Contract Property" means a real estate property that a Company has
     agreed to purchase directly or indirectly (through the purchase of Stock)
     from a Person that is not a Company.

          "Development Property" means a real estate property that is under
     construction or development by a Person that is not a Company and that a
     Company has agreed to purchase or lease (pursuant to a master lease or
     ground lease of all or substantially all of the property) upon completion
     of such construction or development.

          "Excluded Companies" means, as of any date of determination, any
     Consolidated Affiliate or Unconsolidated Affiliate of PPT determined in a
     manner reasonably acceptable to Agents whose (a) individual contribution to
     the calculation of Total Assets as of such determination date constitutes
     less than fifteen percent (15%) of Total Assets, and (b) aggregate
     contributions to the calculation of Total Assets as of such determination
     date constitute less than twenty percent (20%) of Total Assets.

          "Investments in Joint Ventures" means the Companies' investments in
     the Stock of, or loans and advances to, partnerships, joint ventures, and
     similar entities that are not Consolidated Affiliates. Investments in Joint
     Ventures, as of any date, shall be calculated as the lesser of the
     Companies' Share of (a) the Approved Costs of each Property owned by an
     Unconsolidated Affiliate, and (b) the sum of (i) the book value of such
     Property on the financial statements of such Unconsolidated Affiliate
     determined in accordance with GAAP plus (ii) accumulated depreciation with
     respect to such Property determined in accordance with GAAP.
          "Redemption" means, with respect to any Stock issued by a Person, the
     retirement, redemption, purchase, or other acquisition for value of such
     Stock by such Person.

          "Stock" means all shares, options, warrants, general or limited
     partnership interests, membership interests, or other ownership interests
     (regardless of how designated) of or in a corporation, partnership, limited
     liability company, trust, or other entity, whether voting or nonvoting,
     including common stock, preferred stock, or any other "equity security" (as
     such term is defined in Rule 3a11-1 of the General Rules and Regulations
     promulgated by the Securities and Exchange Commission under the Securities
     Exchange Act of 1934, as amended).

          "Unfunded Liabilities" means, for any Person, (a) if evidenced by a
     Binding Agreement, then

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     all obligations to purchase a Contract Property or Development Property
     (the amount of such Unfunded Liabilities being equal to the Applicable
     Amount with respect to such Contract Property or Development Property), and
     (b) any guaranties, endorsements, and other contingent obligations
     (including any obligations as general partner) with respect to the
     principal of the Liabilities of others (including any Unconsolidated
     Affiliates of such Person) for which such Person has personal liability.

     (c) Section 8.5 is hereby deleted in its entirety and replaced with the
following:

          8.5 Loans, Advances, and Investments. Without the prior written
     consent of the Required Lenders, no Company shall have or make any
     investments in:

          (a) Properties consisting of raw land exceeding in the aggregate five
     percent (5%) of Total Assets;

          (b) Properties under construction having actual and budgeted costs
     exceeding in the aggregate twenty percent (20%) of Total Assets (including
     the total budgeted project costs for all Properties under construction);
     provided that the Companies may not have Properties under construction that
     are less than fifty percent (50%) pre-leased having actual and budgeted
     costs exceeding in the aggregate fifteen percent (15%) of Total Assets
     (including the total budgeted project costs for all Properties under
     construction);

          (c) Except for Borrower's investment in Broadmoor, Investments in
     Joint Ventures exceeding in the aggregate twenty percent (20%) of Total
     Assets;

          (d) Loans, mortgages, advances, and extensions of credit to Persons
     exceeding in the aggregate ten percent (10%) of Total Assets;

          (e) The Stock of Persons that are neither Consolidated Affiliates nor
     Investments in Joint Ventures exceeding in the aggregate five percent (5%)
     of Total Assets; or

          (f) The investments described in (a) through (e) above exceeding in
     the aggregate (without duplication) thirty percent (30%) of the sum of (i)
     Total Assets, and (ii) to the extent not included in the calculation of
     Total Assets, budgeted project costs for all Properties under construction.

     (d) Section 8.6 is hereby deleted in its entirety and replaced with the
following:

          8.6 Distributions and Redemptions. Borrower shall not, and shall not
     permit any Company to, declare, make, or pay any Distribution other than
     (a) Permitted Distributions, (b) Distributions declared, made, or paid by
     (i) any Company wholly in the form of its Stock, and (ii) any Company
     (other than Borrower) to Borrower or to PPT, and (c) Distributions paid to
     the holders of PPT's Stock who simultaneously use the proceeds of such
     Distributions to purchase additional shares of PPT's Stock pursuant to a
     dividend reinvestment program; provided that the amount of any
     Distributions made pursuant to clauses (b) and (c) shall not be limited by
     clause (a). Borrower shall not, and shall not permit any Company to,
     declare, make, or pay any Redemptions (net of the amount of any Net
     Proceeds from the resale of Stock previously redeemed pursuant to a
     Permitted Redemption) other than Permitted Redemptions. Borrower shall not,
     and shall not permit any Company to, enter into or permit to exist any
     arrangement or agreement (other than this

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     Agreement, the Existing Line of Credit, and that certain Credit Agreement
     dated as of October 13, 1998, executed by Borrower, Dresdner Bank AG, New
     York Branch and Grand Cayman Branch, as Administrative Agent and
     Syndication Agent, the Documentation Agent defined therein, and the Lenders
     defined therein, as modified, amended, renewed, extended, and restated from
     time to time) that prohibits it from paying Distributions to its
     shareholders, partners, or members. Nothing in this Section 8.6 restricts
     the issuance by any Company of preferred Stock solely because such Stock
     requires the payment of Distributions with respect to such Stock prior to
     the payment of Distributions with respect to common Stock.

     (e) Section 9 is hereby deleted in its entirety and replaced with the
following:

                                    SECTION 9

                               FINANCIAL COVENANTS

          Until the Obligation is paid and performed in full, Borrower covenants
     and agrees with Administrative Agent and Lenders that Borrower shall not
     directly or indirectly permit:

          9.1 Minimum Tangible Net Worth. As of any date, the Tangible Net Worth
     to be less than (a) $1,000,000,000, plus (b) eighty percent (80%) of the
     amount of Net Proceeds of any Equity Issuances subsequent to May 23, 2000,
     minus (c) eighty percent (80%) of the amount of any Permitted Redemptions
     subsequent to May 23, 2000.

          9.2 Total Indebtedness to Total Assets. As of any date, the ratio of
     (a) all Indebtedness of the Companies, on a consolidated basis, to (b)
     Total Assets to exceed 0.55 to 1.0.

          9.3 Maximum Secured Debt. As of any date, the ratio of (a) Secured
     Debt of the Companies, on a consolidated basis, to (b) Total Assets to
     exceed 0.475 to 1.0.

          9.4 Recourse Debt. As of any date, the Companies, individually or on a
     consolidated basis, to incur, guarantee, or otherwise be or become,
     directly or indirectly, liable in respect of any Recourse Debt (other than
     Permitted Recourse Debt).

          9.5 Interest and Debt Service Coverage Ratios.

          (a) As of any date, the ratio of (i) Aggregate EBITDA, to (ii)
     Interest Expense of the Companies, on a consolidated basis, in each case
     for the twelve (12) month period ending on the date of determination, to be
     less than 2.0 to 1.0. For purposes of the foregoing, Aggregate EBITDA and
     Interest Expense shall include each Company's (as the case may be, but
     without duplication) Share of Aggregate EBITDA and Interest Expense of
     their respective Unconsolidated Affiliates.

          (b) As of any date, the ratio of (i) (A) Aggregate EBITDA, minus (B)
     Non-Incremental Capital Expenditures (other than of Broadmoor), to (ii)
     Debt Service, in each case for the twelve (12) month period ending on the
     date of determination, to be less than 1.75 to 1.0. For purposes of the
     foregoing, Aggregate EBITDA, Non-Incremental Capital Expenditures, and Debt
     Service shall include each Company's (as the case may be, but without
     duplication) Share of Aggregate EBITDA, Non-Incremental Capital
     Expenditures, and Debt Service of their respective Unconsolidated
     Affiliates.

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          (c) As of any date, the ratio of (i) Adjusted Aggregate EBITDA, to
     (ii) Fixed Charges, in each case for the twelve (12) month period ending on
     the date of determination, to be less than 1.6 to 1.0.

     For purposes of calculating any of the financial covenants in this Section
     9, (x) (i) Indebtedness shall not include any Indebtedness of any Company
     that has been defeased, (ii) Total Assets shall not include any assets of
     any Company that have been used to defease any Indebtedness of any Company,
     (iii) Aggregate EBITDA and other income items shall not include any income
     on or with respect to any assets of any Company that have been used to
     defease any Indebtedness of any Company, and (iv) Interest Expense shall
     not include any Interest Expense with respect to any Indebtedness that has
     been defeased (except to the extent that such Interest Expense exceeds any
     income excluded pursuant to clause (iii)); provided that the aggregate
     principal amount of all Indebtedness that has been defeased shall not
     exceed $100,000,000 at any time outstanding without the prior written
     consent of each Agent, and (y) the definitions of Adjusted Aggregate
     EBITDA, Indebtedness, Secured Debt, Recourse Debt, Aggregate EBITDA,
     Interest Expense, Non-Incremental Capital Expenditures, Debt Service,
     Unsecured Debt, and Fixed Charges shall include (without duplication) the
     Companies' Share of such amounts for their Unconsolidated Affiliates (other
     than Broadmoor).

     (e) Section 13.9(f) of the Credit Agreement is hereby deleted in its
entirety and replaced with the following:

          (f) Existing Line of Credit. If the provisions of the Existing Line of
     Credit that correspond to Section 8.5, 8.6, or 9, or any of the defined
     terms used therein, of this Agreement are modified or amended, then
     Borrower and the Credit Parties agree that such Sections and defined terms
     in this Agreement shall be automatically (and without the necessity of a
     separate modification, amendment, or agreement) modified or amended to
     conform to such provisions in the Existing Line of Credit; provided that no
     amendment to the Existing Line of Credit shall result in a modification or
     amendment of Section 9.3 of this Agreement in a manner that increases the
     maximum permitted ratio of Secured Debt to Total Assets to more than 0.475
     to 1.0.

     2. Amendment of Credit Agreement and Other Loan Documents.

     (a) All references in the Loan Documents to the Credit Agreement shall
henceforth include references to the Credit Agreement as modified and amended by
this Amendment, and as may, from time to time, be further modified, amended,
restated, extended, renewed, and/or increased.

     (b) Any and all of the terms and provisions of the Loan Documents are
hereby amended and modified wherever necessary, even though not specifically
addressed herein, so as to conform to the amendments and modifications set forth
herein.

     3. Ratifications. Borrower (a) ratifies and confirms all provisions of the
Loan Documents as amended by this Amendment, (b) ratifies and confirms that all
guaranties, assurances, and Liens granted, conveyed, or assigned to the Credit
Parties under the Loan Documents are not released, reduced, or otherwise
adversely affected by this Amendment and continue to guarantee, assure, and
secure full payment and performance of the present and future Obligation, and
(c) agrees to perform such acts and duly authorize, execute, acknowledge,
deliver, file, and record such additional documents, and certificates as the
Credit Parties

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may reasonably request in order to create, perfect, preserve, and protect those
guaranties, assurances, and Liens.

     4. Representations. Borrower represents and warrants to the Credit Parties
that as of the date of this Amendment: (a) this Amendment and the other
documents executed in connection therewith (collectively, the "Amendment
Documents") have been duly authorized, executed, and delivered by Borrower and
each of the other Companies that are parties to the Amendment Documents; (b) no
action of, or filing with, any Governmental Authority is required to authorize,
or is otherwise required in connection with, the execution, delivery, and
performance by Borrower or PPT of the Amendment Documents to which they are a
party; (c) the Loan Documents, as amended by the Amendment Documents, are valid
and binding upon Borrower and the other Companies that are parties to the
Amendment Documents and are enforceable against Borrower and PPT in accordance
with their respective terms, except as limited by Debtor Relief Laws and general
principles of equity; (d) the execution, delivery, and performance by Borrower
and PPT to which they are a party of the Amendment Documents do not require the
consent of any other Person and do not and will not constitute a violation of
any Governmental Requirement, order of any Governmental Authority, or material
agreements to which Borrower or any other Company is a party thereto or by which
Borrower or any other Company is bound; (e) all representations and warranties
in the Loan Documents are true and correct in all material respects on and as of
the date of this Amendment, except to the extent that (i) any of them speak to a
different specific date, or (ii) the facts on which any of them were based have
been changed by transactions contemplated or permitted by the Credit Agreement;
and (f) both before and after giving effect to the Amendment Documents, no
Potential Default or Default exists.

     5. Conditions. This Amendment and the other Amendment Documents shall not
be effective unless and until:

     (a) this Amendment and the other Amendment Documents have been executed by
Borrower, PPT, Administrative Agent, and the Required Lenders;

     (b) the representations and warranties in this Amendment are true and
correct in all material respects on and as of the date of this Amendment, except
to the extent that (i) any of them speak to a different specific date, or (ii)
the facts on which any of them were based have been changed by transactions
contemplated or permitted by the Credit Agreement; and

     (c) both before and after giving effect to this Amendment, no Potential
Default or Default exists.

     6. Continued Effect. Except to the extent amended hereby or by any
documents executed in connection herewith, all terms, provisions, and conditions
of the Credit Agreement and the other Loan Documents, and all documents executed
in connection therewith, shall continue in full force and effect and shall
remain enforceable and binding in accordance with their respective terms.

     7. Miscellaneous. Unless stated otherwise (a) the singular number includes
the plural and vice versa and words of any gender include each other gender, in
each case, as appropriate, (b) headings and captions may not be construed in
interpreting provisions, (c) this Amendment shall be construed -- and its
performance enforced -- under Texas law, (d) if any part of this Amendment is
for any reason found to be unenforceable, all other portions of it nevertheless
remain enforceable, and (e) this Amendment may be executed in any number of
counterparts with the same effect as if all signatories had signed the same
document, and all of those counterparts must be construed together to constitute
the same document.

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     8. Parties. This Amendment binds and inures to Borrower and the Credit
Parties and their respective successors and permitted assigns.

     9. Entireties. The Credit Agreement AND THE OTHER Loan Documents, AS
AMENDED BY THIS Amendment AND THE OTHER Amendment DOCUMENTS, REPRESENT THE FINAL
AGREEMENT BETWEEN THE PARTIES ABOUT THE SUBJECT MATTER OF THE Credit Agreement
AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS, OR SUBSEQUENT
ORAL AGREEMENTS OF THE PARTIES. There ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN
THE PARTIES.

                  [Remainder of Page Intentionally Left Blank;
                           Signature Pages to Follow.]

                                       10

<PAGE>

                      SIGNATURE PAGE TO FIRST AMENDMENT OF
                            CREDIT AGREEMENT BETWEEN
                 PRENTISS PROPERTIES ACQUISITION PARTNERS, L.P.,
                 BANK ONE, TEXAS, N.A., AS ADMINISTRATIVE AGENT,
                  THE CO-DOCUMENTATION AGENTS DEFINED THEREIN,
                         AND THE LENDERS DEFINED THEREIN

EXECUTED as of the day and year first mentioned.

                            PRENTISS  PROPERTIES  ACQUISITION  PARTNERS, L.P.,
                            a Delaware  limited partnership,
                            as Borrower

                            By:      PRENTISS PROPERTIES I, INC.,
                                     General Partner

                                     By: /s/ Richard C. Bower
                                         ---------------------------------------
                                         Richard C. Bower
                                         Vice President

<PAGE>

                      SIGNATURE PAGE TO FIRST AMENDMENT OF
                            CREDIT AGREEMENT BETWEEN
                 PRENTISS PROPERTIES ACQUISITION PARTNERS, L.P.,
                 BANK ONE, TEXAS, N.A., AS ADMINISTRATIVE AGENT,
                  THE CO-DOCUMENTATION AGENTS DEFINED THEREIN,
                         AND THE LENDERS DEFINED THEREIN

                            BANK ONE, TEXAS, N.A.,
                            as Administrative Agent and a Lender

                            By:          /s/ Roderick Washington
                                ------------------------------------------------
                                Name:       Roderick Washington
                                Title:      First Vice President

<PAGE>

                      SIGNATURE PAGE TO FIRST AMENDMENT OF
                            CREDIT AGREEMENT BETWEEN
                 PRENTISS PROPERTIES ACQUISITION PARTNERS, L.P.,
                 BANK ONE, TEXAS, N.A., AS ADMINISTRATIVE AGENT,
                  THE CO-DOCUMENTATION AGENTS DEFINED THEREIN,
                         AND THE LENDERS DEFINED THEREIN

                            MELLON BANK, N.A.,
                            as a Co-Documentation Agent and a Lender

                            By:              /s/ David W. Tetrick
                                ------------------------------------------------
                                Name:        David W. Tetrick
                                Title:       Vice President

<PAGE>

                      SIGNATURE PAGE TO FIRST AMENDMENT OF
                            CREDIT AGREEMENT BETWEEN
                 PRENTISS PROPERTIES ACQUISITION PARTNERS, L.P.,
                 BANK ONE, TEXAS, N.A., AS ADMINISTRATIVE AGENT,
                  THE CO-DOCUMENTATION AGENTS DEFINED THEREIN,
                         AND THE LENDERS DEFINED THEREIN

                            UNION BANK OF CALIFORNIA, N.A.,
                            as a Co-Documentation Agent and a Lender

                            By:               /s/ Kevin Jordan
                                ------------------------------------------------
                                Name:         Kevin Jordan
                                Title:        Vice President

<PAGE>

     To induce the Credit Parties to enter into this Amendment, the undersigned
(a) consents and agrees to the Amendment Documents' execution and delivery, (b)
ratifies and confirms that all guaranties, assurances, and Liens granted,
conveyed, or assigned to the Credit Parties under the Loan Documents are not
released, diminished, impaired, reduced, or otherwise adversely affected by the
Amendment Documents and continue to guarantee, assure, and secure the full
payment and performance of all present and future Obligation (except to the
extent specifically limited by the terms of such guaranties, assurances, or
Liens), (c) agrees to perform such acts and duly authorize, execute,
acknowledge, deliver, file, and record such additional guaranties, assignments,
security agreements, deeds of trust, mortgages, and other agreements, documents,
instruments, and certificates as the Credit Parties may reasonably deem
necessary or appropriate in order to create, perfect, preserve, and protect
those guaranties, assurances, and Liens, and (d) waives notice of acceptance of
this consent and agreement, which consent and agreement binds the undersigned
and its successors and permitted assigns and inures to the Credit Parties and
their respective successors and permitted assigns.

                            PRENTISS PROPERTIES TRUST, a Maryland real estate
                            investment trust

                            By:               /s/ Michael A. Ernst
                                ------------------------------------------------
                                Name:         Michael A. Ernst
                                Title:        Senior Vice President
                                              Chief Financial Officer

                                       15<PAGE>

                                                                   Exhibit 10.30

                                 LOAN AGREEMENT

     THIS LOAN AGREEMENT (this "Agreement") is made and entered into as of June
30, 1999, by and between Prentiss Properties Acquisition Partners, L.P., a
Delaware limited partnership (the "Lender"), and Bob Wiberg, an individual
residing at the address listed below (the "Borrower," and together with the
Lender, the "Parties").

                             PRELIMINARY STATEMENTS
                             ----------------------

     A. The Lender desires to lend funds to the Borrower in accordance with the
terms and conditions set forth in this Agreement which provides for loan
forgiveness in specified increments upon certain conditions with the purpose of
securing the continued and future employment services of certain key management
officers of the Lender, upon whose involvement, initiative and efforts the
Lender is largely dependent for the successful conduct of its business.

     B. The Borrower is now employed or engaged by the Lender or one of its
affiliates in a key employee capacity, and the Lender desires him or her to
remain in such capacity. The Borrower desires to borrow funds from the Lender in
accordance with the terms and conditions set forth in this Agreement.

     NOW, THEREFORE, in consideration of the premises and the mutual agreements
contained herein, and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties intending to be
legally bound, hereby agree as follows:

                             STATEMENT OF AGREEMENT
                             ----------------------

     Section 1. Loan. Subject to the terms and conditions of this Agreement, the
                ----
Lender agrees to loan (the "Loan") to the Borrower an aggregate amount not to
exceed THREE HUNDRED FIFTY THOUSAND DOLLARS ($350,000.00). The Loan will be
evidenced by a promissory note of the Borrower, substantially in the form of
Exhibit A attached hereto and incorporated herein for all purposes (the "Note"),
---------
with payment terms, interest rate, and other terms as set forth therein. The
Loan shall be made by Lender to Borrower within ten (10) days from the date this
Agreement is signed by the Borrower.

     Section 2. Use of Funds. The funds provided by the Loan (the "Funds") shall
                ------------
be used by the Borrower for such lawful purposes as the Borrower, in its sole
discretion, deems appropriate, provided, however, the Borrower shall not use the
Funds for any purpose which would violate any of the provisions of this
Agreement or the terms of Borrower's employment with the Lender (including any
policies of the Lender in effect from time to time).

     Section 3. Conditions to Funding. The Lender's obligation to fund the Loan
                ---------------------
is expressly conditioned upon the Borrower's execution and delivery of the
following documents to the Lender prior to the funding of the Loan:

          (a) this Agreement; and

<PAGE>

          (b) the Note.

     Section 4. Payments. The Borrower agrees that all payments to be made on or
                --------
in connection with the Note shall be made to the Lender at the address set forth
in this Agreement or such other place as Lender may designate in writing. All
payments referred to under this Agreement and the Note shall be in immediately
available funds in lawful money of the United States of America. Whenever any
payment to be made under this Note shall be stated to be due on a day that is
not a business day, the due date thereof shall be extended to the next
succeeding business day, and, with respect to the payment of principal, interest
thereon shall be payable at the applicable rate during such extension. Each
payment received by the Lender shall be applied first to late charges and
collection expenses, if any, then to the payment of accrued but unpaid interest
due hereunder, and then to the reduction of the unpaid principal balance hereof.

     Section 5. Loan Forgiveness. As long as the Borrower is still employed with
                ----------------
the Lender, and not in breach of the terms of this Agreement or the Note, the
principal of the Note will be forgiven as follows:

          (a) the lesser of (i) one-third of the original principal amount of
     the Note and (ii) the remaining unpaid principal amount of the Note will be
     forgiven at the third anniversary of the date of the Note if the Borrower
     has been continuously employed by the Lender during the period beginning on
     the date of the Note and ending on the third anniversary thereof; provided,
     however, that this Section 5(a) shall not apply if, as of such third
     anniversary date, any Event of Default described in Section 7(c) of the
     Note has occurred;

          (b) the lesser of (i) one-third of the original principal amount of
     the Note and (ii) the remaining unpaid principal amount of the Note will be
     forgiven at the fourth anniversary of the date of the Note if the Borrower
     has been continuously employed by the Lender during the period beginning on
     the date of the Note and ending on the fourth anniversary thereof;
     provided, however, that this Section 5(b) shall not apply if, as of such
     fourth anniversary date, any Event of Default described in Section 7(c) of
     the Note has occurred; and

          (c) the remaining principal amount of the Note will be forgiven at the
     fifth anniversary of the date of the Note if the Borrower has been
     continuously employed by the Lender during the period beginning on the date
     of the Note and ending on the fifth anniversary thereof; provided, however,
     that this Section 5(c) shall not apply if, as of such fifth anniversary
     date, any Event of Default described in Section 7(c) of the Note has
     occurred.

     Section 6. Representations and Warranties. In order to induce the Lender to
                ------------------------------
enter into this Agreement and to make the Loan to the Borrower, the Borrower
hereby represents and warrants to the Lender, as of the date hereof, that this
Agreement and the Note when executed and delivered by the Borrower will be
legal, valid and binding obligations of the Borrower, enforceable against the
Borrower in accordance with their respective terms.

                                       2

<PAGE>

     Section 7. Tax Withholding and Right of Setoff. The Borrower agrees to pay
                -----------------------------------
to the Lender upon its demand, such amount as may be requested by the Lender for
the purpose of satisfying Lender's liability to withhold federal, state, or
local income or other taxes incurred by reason of any forgiveness of any portion
of the Note. The Borrower hereby grants to Lender the right and agrees that the
Lender shall be entitled, at its option and upon written notice to the Borrower,
to offset balances owed by the Lender to the Borrower, whether related to
salary, bonus, expense reimbursement or otherwise, first against any late
charges and collection expenses, if any, then against any accrued but unpaid
interest due, and then to the unpaid principal balance of the Note.

     Section 8. Continued Employment or Retention. Nothing in this Agreement
                ---------------------------------
shall confer upon the Borrower any right to continue in the employment of the
Lender or any affiliate, or interfere with or limit in any way the right of the
Lender or any affiliate to terminate the Borrower's employment at any time.
Nothing in this Agreement shall create an employment agreement between Borrower
and Lender.

     Section 9. GOVERNING LAW. THIS AGREEMENT HAS BEEN DELIVERED TO AND ACCEPTED
                -------------
BY THE BORROWER IN THE STATE OF TEXAS, AND SHALL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE SUBSTANTIVE LAWS OF THE STATE OF TEXAS WITHOUT GIVING EFFECT
TO THE CHOICE OF LAW OR CONFLICT OF LAWS RULES THEREOF.

     Section 10. Assignment. The Borrower may not assign this Agreement or the
                 ----------
Note without the prior written consent of the Lender.

     Section 11. Counterparts. This Agreement may be executed in any number of
                 ------------
counterparts, each of which shall be deemed to be an original, and all of which
together shall constitute one and the same agreement notwithstanding that all
parties are not signatories to each individual counterpart.

     Section 12. Limitation on Interest. Notwithstanding anything to the
                 ----------------------
contrary in this Agreement, the Note or in any document evidencing the
indebtedness evidenced hereby or in any other agreement entered into in
connection herewith, whether now existing or hereafter arising, it is agreed
that the aggregate of all interest and other charges constituting interest, or
adjudicated as constituting interest, and contracted for, chargeable or
receivable under the Note or otherwise in connection with this transaction shall
under no circumstances ever exceed the maximum nonusurious interest rate allowed
under applicable law (the "Maximum Rate"). If fulfillment of any provision
hereof or of any document evidencing or securing the indebtedness contemplated
hereby, at the time performance of such provision shall be due, shall involve
transcending the Maximum Rate, then, ipso facto, the obligation to be fulfilled
shall be reduced to the Maximum Rate; and if the Lender shall ever receive
anything of value deemed interest under applicable law which would exceed the
Maximum Rate, an amount equal to any excessive interest shall be applied to the
reduction of the principal amount owing to the Lender and not to the payment of
interest, or if such excessive interest exceeds the unpaid balance of principal
hereof, such excess shall be refunded to the Borrower. All sums paid or agreed
to be paid to the Lender for the use, forbearance or detention of the
indebtedness of the Borrower to the Lender shall, to the extent permitted by
applicable law, be amortized, prorated, allocated and spread throughout the full
term of such

                                       3

<PAGE>

indebtedness until payment in full so that the rate of interest on account of
such indebtedness shall not exceed the maximum amount permitted by applicable
law. The term "applicable law" as used herein shall mean the laws of the State
of Texas or the laws of the United States, whichever laws allow the greater rate
of interest, as such laws now exist or may be changed or amended to come into
effect in the future. The provisions of this paragraph shall control and
supersede all agreements between the Borrower and the Lender.

     Section 13. Headings. The descriptive headings contained in this Agreement
                 --------
are inserted for convenience only and do not constitute a substantive part of
the Agreement.

     Section 14. Amendment. This Agreement may be amended, modified, superseded
                 ---------
or cancelled, any term or condition hereof may be waived, only by a written
instrument executed by Lender and Borrower at such time.

     Section 15. No Waivers. The failure of either party at anytime or times to
                 ----------
require performance of any provisions hereof shall in no manner affect the right
at a later time to enforce the same. No waiver by either party of any condition,
or of any breach of any term contained in this Agreement, in any one or more
instances, shall be deemed to be or construed as further or continuing waiver of
any such condition or breach or a waiver of any other condition of any breach of
any other term, covenant, representation or warranty.

     Section 16. Pronouns. Whenever a pronoun of a particular gender is used in
                 --------
this Agreement, if appropriate that pronoun also will refer to the other gender
and the neuter. Whenever a neuter pronoun is used in this Agreement, if
appropriate that pronoun also will refer to the masculine and feminine gender.

                            [SIGNATURE PAGE FOLLOWS]

                                       4

<PAGE>

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

                              LENDER:

                              PRENTISS PROPERTIES AQUISITION PARTNERS, L.P.

                              By: Prentiss Properties I, Inc., General Partner

                                  By: /s/ Thomas F. August
                                      ----------------------------------------
                                      Thomas F. August
                                      President

                              BORROWER:

                              /s/ Bob Wiberg
                              --------------------------------------------------
                              Bob Wiberg

                              3890 W. Northwest Highway, Suite 400

                                       5

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