SALES AGREEMENT

Exhibit 1.1

PRENTISS PROPERTIES TRUST

DOCS ^® Financing Program

2,000,000 Shares of Beneficial Interest,

$0.01 par value

SALES AGREEMENT

May 28, 2004

DOCS ^® is a registered service mark of Brinson Patrick Securities Corporation

TABLE OF CONTENTS

THIS SALES AGREEMENT (the “Agreement”) dated as of May 28, 2004 between Brinson Patrick Securities Corporation, having its principal office at 330 Madison Avenue, 9 ^th Floor, New York, New York 10017 (the “Sales Manager”) and Prentiss Properties Trust, a Maryland real estate investment trust (the ”Company”).

WHEREAS , the Company and the Sales Manager have previously entered into that certain sales agreement, dated as of June 10, 2002 for the issuance and sale of up to 3,000,000 of the Company’s common shares of beneficial interest, par value $0.01 per share (the “Original Sales Agreement”);

WHEREAS , after issuance and sale of all shares issuable under the Original Sales Agreement, the Company desires to issue and sell through the Sales Manager up to an additional 2,000,000 shares (the “Maximum Amount”) of its common shares of beneficial interest, par value $0.01 per share (the ”Shares”), on the terms and subject to the conditions set forth in this Agreement. The Maximum Amount shall be appropriately shall be adjusted for share splits and reverse splits; and

WHEREAS , this Agreement shall govern solely the issuance and sale of the additional 2,000,0000 Shares that are the subject of this Agreement, and does not relate to or govern the issuance and sale of the Company’s common shares pursuant to the Original Sales Agreement.

IN CONSIDERATION of the mutual covenants contained in this Agreement, the Company and the Sales Manager agree as follows:

ARTICLE I.

REPRESENTATIONS AND WARRANTIES

OF THE COMPANY

1.1    For purposes of this Agreement, unless the context requires to the contrary, the term “Significant Subsidiary” includes all significant subsidiaries (as defined by Section 1-02 of Regulation S-X) of the Company. The Company makes all of the representations, warranties and agreements set forth below as of the date the Registration Statement (as defined below) is declared effective, and as of each date that the Sales Manager is selling shares pursuant to this Agreement. In addition, the Company makes the representations, warranties and agreement in paragraphs f, g, h, i, j, m, n, o, r, s, t, v, w, x, y, z, aa and bb below, as of the date of this Agreement.

(a)    The Company meets the requirements for use of Form S-3 under the Securities Act of 1933, as amended (the “Act”), and the rules and regulations thereunder (“Rules and Regulations”). A registration statement on Form S-3 with respect to, among other securities, the Shares, including a form of prospectus, will be prepared by the Company in conformity with the requirements of the Act and the Rules and Regulations and will be filed with the Securities and Exchange Commission (the “Commission”) as provided in Section 3.1 hereto. Copies of such registration statement and prospectus, any such amendment or supplement thereto and all documents incorporated by reference therein that are filed with the Commission shall be

delivered to the Sales Manager or will be made available to the Sales Manager on the Commission’s internet website. Such registration statement, as of the date it is declared effective by the Commission, and as it may thereafter be amended, is referred to herein as the “Registration Statement,” and the final form of prospectus included in the Registration Statement for purposes of offers and sales of the Shares contemplated herein, as amended or supplemented from time to time, is referred to herein as the “Prospectus.” The preliminary registration statement as filed with the Commission on the date hereof is referred herein as the “Preliminary Registration Statement.” Any reference herein to the Registration Statement, the Prospectus, Preliminary Registration Statement or any amendment or supplement thereto shall be deemed to refer to and include the documents incorporated (or deemed to be incorporated) by reference therein, and any reference herein to the terms “amend,” “amendment” or “supplement” with respect to the Registration Statement or Prospectus shall be deemed to refer to and include the filing after the execution hereof of any document with the Commission deemed to be incorporated by reference therein.

(b)    Each part of the Registration Statement, when such part becomes effective, and the Prospectus and any amendment or supplement thereto, on the date such amendment or supplement is filed with the Commission and at each Settlement Date (as hereinafter defined), will conform in all material respects with the requirements of the Act and the Rules and Regulations; each part of the Registration Statement, when such part becomes effective, will not contain an untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading; and the Prospectus and any amendment or supplement thereto, on the date such amendment or supplement is filed with the Commission and at each Settlement Date, will not include an untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading; except that the foregoing shall not apply to statements in or omissions from any such document in reliance upon, and in conformity with, written information furnished to the Company by or on behalf of the Sales Manager, specifically for use in the Registration Statement, the Prospectus or any amendment or supplement thereto.

(c)    The documents incorporated by reference in the Registration Statement or the Prospectus, or any amendment or supplement thereto, when such amendment or supplement is filed with the Commission under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), will conform in all material respects with the requirements of the Act or the Exchange Act, as applicable, and the rules and regulations of the Commission thereunder.

(d)    The financial statements of the Company, together with the related schedules and notes thereto, set forth or included in the Registration Statement or the Prospectus, fairly present in all material respects the financial condition of the Company as of the dates indicated and the results of operations, changes in financial position, stockholders’ equity, and cash flows for the periods therein specified, and have been prepared in conformity with generally accepted accounting principles consistently applied throughout the periods involved (except as otherwise stated therein). The summary and selected financial and statistical data included in the Registration Statement or the Prospectus present fairly the information shown therein and, to the extent based upon or derived from the financial statements, have been compiled on a basis consistent with the financial statements presented therein.

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(e)    PricewaterhouseCoopers L.L.P., who will certify the financial statements included in the Registration Statement are and, during the periods covered by their reports, were qualified and independent public accountants as required by Rule 2-01 of Regulation S-X.

(f)    The Company has been duly organized and is validly existing as a real estate investment trust in good standing under the laws of the State of Maryland. The Company is duly qualified and in good standing in each jurisdiction in which the character or location of its assets or properties (owned, leased or licensed) or the nature of its business makes such qualification necessary (including every jurisdiction in which it owns or leases real property), except for such jurisdictions where the failure to so qualify would not have a Material Adverse Effect. For purposes of this Agreement, “Material Adverse Effect” means any adverse effect on the business, operations, properties or financial condition of the Company and all of its subsidiaries taken as a whole that is material to the Company and all of its subsidiaries taken as a whole, and any material adverse effect on the transactions contemplated under this Agreement or any other agreement or document contemplated hereby or thereby. Each Significant Subsidiary is validly existing as a corporation, limited liability company or partnership, as applicable, in its respective jurisdiction of formation. Schedule 1.1(f) hereto identifies each of the Company’s subsidiaries that is a “Significant Subsidiary” (as defined in Section 1-02 of Regulation S-X) of the Company. All of the issued and outstanding capital stock, limited liability company interests or partnership interests, as applicable, of each Significant Subsidiary has been duly authorized and validly issued, is fully paid and nonassessable and (except as otherwise disclosed or incorporated by reference in the Registration Statement or the Prospectus or the Preliminary Registration Statement) is owned by the Company, directly or indirectly, free and clear of any security interest, mortgage, pledge, lien, encumbrance, claim or equity. Except as disclosed or incorporated by reference in the Registration Statement or the Prospectus or Preliminary Registration Statement, the Company does not own, lease or license any asset or property or conduct any business outside the United States of America. The Company has all requisite power and authority and all necessary authorizations, approvals, consents, orders, licenses, certificates and permits of and from all governmental orders or regulatory bodies or any other person or entity having jurisdiction over the Company, to own, lease, license and operate its assets and properties and conduct its business as now being conducted and as described or incorporated by reference in the Registration Statement or the Prospectus or the Preliminary Registration Statement; except for such authorizations, approvals, consents, orders, licenses, certificates and permits the absence of which would not have a Material Adverse Effect; and no such authorization, approval, consent, order, license, certificate or permit contains a materially burdensome restriction other than as disclosed in the Registration Statement or the Prospectus or the Preliminary Registration Statement.

(g)    The Company has good and marketable title to, or leasehold interests in, all properties and assets (including, without limitation, mortgaged assets) as described in the Registration Statement or the Prospectus or the Preliminary Registration Statement owned by the Company, free and clear of all liens, charges, encumbrances or restrictions, except such as are described or incorporated by reference in the Registration Statement or the Prospectus or the Preliminary Registration Statement and except such as would not have a Material Adverse Effect. The Company has such consents, easements, rights-of-way or licenses (collectively, “rights-of-way”) from any person as are necessary to conduct its business in the manner described in the Registration Statement or the Preliminary Registration Statement, except for

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those which if not obtained would not, singly or in the aggregate, have a Material Adverse Effect, and, except as otherwise disclosed or incorporated by reference in the Registration Statement or the Prospectus or Preliminary Registration Statement, none of such rights-of-way contains any restriction that is materially burdensome to the Company.

(h)    The debt financing employed by the Company is not convertible into common shares of the Company or other equity interests in the Company, except as otherwise disclosed or incorporated by reference in the Registration Statement or the Prospectus or Preliminary Registration Statement.

(i)    There is no litigation or governmental or other proceeding or investigation before any court or before or by any public body or board pending to which the Company or any Significant Subsidiary is a party or, to the knowledge of the Company, threatened against, or involving the assets, properties or businesses of the Company that would have a Material Adverse Effect except as described or incorporated by reference in the Registration Statement or Prospectus or Preliminary Registration Statement.

(j)    Except as otherwise disclosed or incorporated by reference in the Registration Statement or the Prospectus or Preliminary Registration Statement, the Company maintains insurance (issued by insurers of recognized financial responsibility) of the types and in the amounts generally deemed adequate for its businesses and, to the knowledge of the Company, consistent with insurance coverage maintained by similar companies in similar businesses, including, but not limited to, insurance covering real and personal property owned or leased by the Company against theft, damage, destruction, acts of vandalism and all other risks customarily insured against, all of which insurance is in full force and effect.

(k)    Subsequent to the respective dates as of which information is given in the Registration Statement or the Prospectus, except as described or incorporated by reference therein, (i) there has not been any material adverse change in the assets or properties, business, results of operations, or condition (financial or otherwise) of the Company and all of its subsidiaries taken as a whole (a “Material Adverse Change”), whether or not arising from transactions in the ordinary course of business; (ii) the Company has not sustained any material loss or interference with its assets, businesses or properties (whether owned or leased) from fire, explosion, earthquake, flood or other calamity, whether or not covered by insurance, or from any labor dispute or any court or legislative or other governmental action, order or decree; (iii) since the date of the latest balance sheet, included or incorporated by reference in the Registration Statement or the Prospectus, except as reflected therein, the Company has not undertaken any material liability or obligation, direct or contingent, except such liabilities or obligations undertaken in the ordinary course of business; and (iv) there has not been any transaction that is material to the Company, except transactions in the ordinary course of business or as otherwise disclosed or incorporated by reference in the Registration Statement or the Prospectus.

(l)    There is no document or contract of a character required by the Exchange Act or by the rules and regulations thereunder to be described in the Registration Statement or the Prospectus or to be filed as an exhibit to the Registration Statement (a “Material Contract”) that is not described or filed as required. Each document, instrument, contract and agreement of the Company described in the Registration Statement or the Prospectus or incorporated by reference

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therein or listed as an exhibit to the Registration Statement is in full force and effect and is valid and enforceable by and against the Company in accordance with its terms, assuming the due authorization, execution and delivery thereof by each of the other parties thereto except as such enforceability may be limited by applicable bankruptcy, insolvency, reorganization or other similar laws affecting creditor’s rights generally and by general equitable principals (regardless of whether enforceability is considered in a proceeding in equity or at law) or except as otherwise disclosed or incorporated by reference in the Registration Statement or Prospectus. Neither the Company nor, to the knowledge of the Company, any other party is in default in the observance or performance of any material term or obligation to be performed under any such agreement, and no event has occurred which with notice or lapse of time or both would constitute such a default, which default or event would have a Material Adverse Effect. No default exists, and no event has occurred which with notice or lapse of time or both would constitute a default, in the due performance and observance of any term, covenant or condition, by the Company of any other agreement or instrument to which the Company is a party or by which it or its properties or business may be bound or affected, which default or event would have a Material Adverse Effect.

(m)    The Company is not in violation of its charter, by-laws or operating agreement, as applicable. The Company is not in violation of any franchise, license, permit, judgment, decree, order, statute, rule or regulation to which it or its properties or assets may be subject, where the consequences of such violation would have a Material Adverse Effect.

(n)    Neither the execution, delivery and performance of this Agreement by the Company nor the consummation by the Company of any of the transactions contemplated hereby (including, without limitation, the issuance and sale by the Company of the Shares) will give rise to a right to terminate or accelerate the due date of any payment due under, or conflict with or result in the breach of any material term or provision of, or constitute a default (or an event which with notice or lapse of time or both would constitute a default) under, or require any consent or waiver under, or result in the execution or imposition of any lien, charge, encumbrance, claim, security interest, restriction or defect upon any properties or assets of the Company pursuant to the terms of, any Material Contract, or any of its material properties or businesses are bound, or any material franchise, license, permit, judgment, decree, order, statute, rule or regulation applicable to the Company or violate any provision of the charter or by-laws of the Company, except for such consents or waivers (i) that have already been obtained and are in full force and effect, (ii) that are required by the listing requirements of the Trading Market (as defined below), (iii) that are required by applicable state securities laws in connection with the purchase and distribution of the Shares, and (iv) the Registration Statement contemplated by Section 3.1(a) below.

(o)    All of the outstanding shares of beneficial interest of the Company have been duly authorized and validly issued and are fully paid and nonassessable and none of the shares were issued in violation of any preemptive or other similar right. The Shares, when issued and sold pursuant to this Agreement, will be duly authorized and validly issued, fully paid and nonassessable and will not be issued in violation of any preemptive or other similar right. Except as disclosed or incorporated by reference in the Registration Statement or the Prospectus or Preliminary Registration Statement, there is no outstanding option, warrant or other right calling for the issuance of, and there is no commitment, plan or arrangement to issue, any capital

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stock of the Company or any security convertible into or exercisable or exchangeable for such capital stock, except for standard dividend reinvestment plans. The Shares conform in all material respects to all statements relating thereto contained in the Registration Statement or the Prospectus.

(p)    Subsequent to the respective dates as of which information is given in the Registration Statement or the Prospectus, (x) except as described or referred to or incorporated by reference therein, (y) except as are not material and are consistent with past practice, and (z) other than (i) regular quarterly dividends and dividends declared and paid in accordance with the terms of any series of preferred shares or units of the Company’s or its Material Subsidiaries, (ii) shares issued pursuant to the Company’s dividend reinvestment plan existing as of the date the Registration Statement is declared effective by the Commission, (iii) shares or options or similar rights to acquire shares issued pursuant to the Company’s employee or trustee stock option or benefit plans or share purchase plans existing as of the date the date the Registration Statement is declared effective by the Commission (iv) shares issued pursuant to the Company’s dividend reinvestment plan existing as of the date of the Registration Statement is declared effective by the Commission, and (v) securities issued pursuant to any other agreement with the Sales Manager, the Company has not (A) issued any securities or (B) declared or paid any dividend or made any distribution on any shares of its capital stock or redeemed, purchased or otherwise acquired or agreed to redeem, purchase or otherwise acquire any shares of its capital stock; provided , however , that the parties acknowledge that included in the Registration Statement or the Prospectus and/or incorporated by reference therein are shares purchased pursuant to a Company share buyback program.

(q)    Except as disclosed or incorporated by reference in the Registration Statement or the Prospectus and other than as provided in the third amended and restated agreement of limited partnership of Prentiss Properties Acquisition Partners, L.P., dated as of October 1, 2001 (as amended, the “Partnership Agreement”), no holder of any security of the Company has the right, which has not been waived, to have any security owned by such holder included in the Registration Statement.

(r)    All necessary trust action has been duly and validly taken by the Company to authorize the execution, delivery and performance of this Agreement and the issuance and sale of the Shares by the Company. This Agreement has been duly and validly authorized, executed and delivered by the Company and, assuming the due authorization, execution and delivery by the Sales Manager, constitutes and will constitute the legal, valid and binding obligation of the Company, enforceable against the Company in accordance with its terms, except as such enforceability may be limited by applicable bankruptcy, insolvency, reorganization or other similar laws affecting creditor’s rights generally and by general equitable principals (regardless of whether enforceability is considered in a proceeding in equity or at law). Except for the Registration Statement contemplated by Section 3.1(a) below (and any “blue sky” filings or Trading Market listing applications to be filed pursuant hereto), each approval, consent, order, authorization, designation, declaration or filing by or with any regulatory, administrative or other governmental body necessary in connection with the execution and delivery by the Company of this Agreement and the consummation of the transactions contemplated hereby and the issuance and sale of the Shares by the Company has been obtained or made and is in full force and effect. The Company will use its best reasonable efforts to cause the Shares to be listed on the Trading

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Market. For purposes of this Agreement, the “Trading Market” is (i) the New York Stock Exchange, Inc., and (ii) each other securities exchange on which the common shares of the Company trade or are admitted for trading.

(s)    The Company has not incurred any liability for a fee, commission or other compensation on account of the employment of a broker or finder in connection with the transactions contemplated by this Agreement other than as contemplated hereby or as described in the Registration Statement or Preliminary Registration Statement.

(t)    The Company is conducting its business in compliance with all applicable laws, rules and regulations of the jurisdictions in which it is conducting business, except where the failure to be so in compliance would not have a Material Adverse Effect and except as otherwise disclosed or incorporated by reference in the Registration Statement or the Prospectus or Preliminary Registration Statement.

(u)    No transaction has occurred between or among the Company and any of its officers or directors or any affiliate or affiliates of any such officer or director that is required to be described, but is not described in, the Registration Statement or the Prospectus.

(v)    The Company has not taken, and will not take, directly or indirectly, any action designed to or which might reasonably be expected to cause or result in, or which has constituted or which might reasonably be expected to constitute, the stabilization or manipulation of the price of the common shares of the Company to facilitate the sale or resale of any of the Shares. The repurchase by the Company of common shares from time to time pursuant to a share repurchase program, shall be conducted in accordance with Rule 10(b)-18 and Regulation M under the Exchange Act.

(w)    The Company has filed all federal, state, local and foreign tax returns that are required to be filed through the date hereof (and will file all such tax returns when and as required to be filed after the date hereof), or has received extensions thereof, and has paid all taxes shown on such returns to be due on or prior to the date hereof (and will pay all taxes shown on such returns to be filed when due after the date hereof) and all assessments received by it to the extent that the same are material and have become due except where the failure to file such a return or pay such amount would not have a Material Adverse Effect.

(x)    The Company has met the qualification requirements for a “real estate investment trust” during its taxable years ending on or after December 31, 1999 and its proposed method of operations will enable it to continue to meet the requirements for qualification and taxation as a “real estate investment trust” under the Internal Revenue Code of 1986, as amended (the “Code”), assuming no change in the applicable underlying law. The Company does not know of the occurrence of any event that would cause or is likely to cause the Company to fail to qualify as a “real estate investment trust” at any time.

(y)    The Company is not an “investment company” within the meaning of the Investment Company Act of 1940, as amended.

(z)    The Company’s system of internal accounting controls complies in all material respects with the listing requirements of the New York Stock Exchange and the Sarbanes-Oxley

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Act of 2002 and the rules promulgated thereunder (provided, that the Company shall not be required to comply with phased-in regulations prior to the date compliance is required by the foregoing rules) and to the best of the Company’s knowledge, neither the Company nor any employee or agent thereof has made any payment of funds of the Company or received or retained any funds, and no funds of the Company have been set aside to be used for any payment, in each case in violation of any law, rule or regulation.

(aa)    The Company is not involved in any labor dispute and, to the knowledge of the Company, no such dispute has been threatened, except for such disputes as would not have a Material Adverse Effect.

(bb)    Except as disclosed or incorporated by reference in the Registration Statement or the Prospectus or the Preliminary Registration Statement, (i) there has been no storage, disposal, generation, manufacture, refinement, transportation, handling or treatment of substances by the Company or any of its subsidiaries (or to the knowledge of the Company, any of their predecessors in interest) at, upon or from any of the property now or previously owned by the Company or its subsidiaries in violation of any applicable law, ordinance, rule, regulation, order, judgment, decree or permit or which would require remedial action under any applicable law, ordinance, rule, regulation, order, judgment, decree or permit, except for any violation or remedial action which would not have a Material Adverse Effect; (ii) there has been no material spill, discharge, leak, emission, injection, escape, dumping or release of any kind onto such property or into the environment surrounding such property of any hazardous substances due to or caused by the Company or any of its subsidiaries, except for any such spill, discharge, leak emission, injection, escape, dumping or release which would not have a Material Adverse Effect; and (iii) the term “hazardous substances” shall have the meanings specified in the federal Comprehensive Environmental Response, Compensation, and Liability Act and similar local, state, federal and foreign laws or regulations with respect to environmental protection.

ARTICLE II.

SALE A