<PAGE>
                    Hines-Sumisei U.S. Core Office Fund, L.P.
                       2800 Post Oak Boulevard, Suite 5000
                              Houston, Texas 77056

__________________, 2004


Hines U.S. Core Office Capital LLC
Hines U.S. Core Office Capital Associates II Limited Partnership
Hines REIT Properties, L.P.
2800 Post Oak Boulevard, Suite 5000
Houston, Texas 77056

         Re:      Rights of Hines REIT Properties, L.P.
                  to acquire an interest and invest in Hines-Sumisei
                  U.S. Core Office Fund L.P.

Ladies and Gentlemen:

                  The purpose of this letter agreement is to document the rights
of Hines REIT Properties, L.P. (together with any wholly-owned subsidiary
thereof, the "Public REIT OP"), a Delaware limited partnership, to acquire an
interest in and to participate in future offerings of Hines-Sumisei U.S. Core
Office Fund, L.P. (the "Partnership"), a Delaware limited partnership.
Capitalized terms used and not otherwise defined herein have the meanings given
to them in the Amended and Restated Agreement of Limited Partnership of the
Partnership as such agreement may be amended from time to time (the "Partnership
Agreement").

                  For good and valuable consideration, the receipt and
sufficiency which are hereby acknowledged, the parties hereto agree as follows:

Initial Purchase Right

                  The Public REIT OP shall have the right and obligation (the
"Initial Investment Right") to acquire a portion of the Capital Interest (as
defined below) in the Partnership held by Hines U.S. Core Office Capital
Associates II Limited Partnership (the "Hines Limited Partner") up to a maximum
amount of $35 million in interest (the "Interest"). To the extent the Public
REIT OP receives net proceeds from the public offering of common shares
contemplated by Hines Real Estate Investment Trust, Inc. or contributed to the
Public REIT OP by Hines Real Estate Holdings Limited Partnership ("Net
Proceeds"), the Public REIT OP shall use all such Net Proceeds to acquire all or
a portion of the Interest. As used herein, the term "Capital Interest" of the
Hines Limited Partner in the Partnership means all right, title and interest of
the Hines Limited Partner in and to the Partnership Units held by it. The Public
REIT OP's right and obligation to acquire the Interest shall terminate on
December 31, 2004. The Hines Limited Partner shall not divest itself of any
portion of its Capital Interest in the Partnership prior to the Termination Date
without the prior consent of the Public REIT OP, except to the extent such
Capital Interest exceeds $35 million in interest plus an amount necessary to
satisfy the Hines Capital Requirement.

<PAGE>

                  The Public REIT OP will deliver all Net Proceeds it receives,
until the Public REIT OP has acquired the entire Interest. The sale of any
portion of the Interest shall be conditioned upon (1) the Public REIT OP
receiving Net Proceeds and (ii) the satisfaction of the conditions to the
transfer of a Partnership Interest set forth in Section 10.5 of the Partnership
Agreement and the execution and delivery of an Investor Questionnaire and
Subscription Agreement by the Public REIT OP to the Partnership in form and
substance reasonably satisfactory to the General Partner.

                  Upon the delivery of any Net Proceeds to the Hines Limited
Partner as contemplated above, the following shall take place:

                  1.  The Public REIT OP shall deliver the applicable Net
                      Proceeds to the Hines Limited Partner by wire transfer of
                      immediately available funds to an account designated by
                      the Hines Limited Partner;

                  2.  The Units associated with the portion of the Interest
                      being acquired by the Public REIT OP (determined by
                      dividing the applicable Net Proceeds delivered by the
                      original per Unit issue price paid for the Units) shall be
                      transferred on the books of the Partnership to the Public
                      REIT OP;

                  3.  The Public REIT OP shall be admitted to the Partnership as
                      a Non-Managing General Partner as contemplated by Section
                      5.11 of the Partnership Agreement and the applicable Units
                      shall automatically be deemed to be non-managing general
                      partner interests in the Partnership; and

                  4.  The General Partner shall amend the Partnership Agreement
                      to the extent necessary to give effect to the foregoing in
                      accordance with the terms of the Partnership Agreement, it
                      being understood that the Public REIT OP will only hold a
                      general partner interest in the Partnership, unless the
                      Public REIT OP agrees to acquire another interest in the
                      Partnership.

<PAGE>

Pre-Emptive Right

                  Following the Initial Offering Period, for so long as the
Public REIT OP is a partner in the Partnership, the Partnership shall give the
Public REIT OP written notice (an "Offer Notice") of any proposed offering of
Units for cash at least 90 days prior to the anticipated closing date of such
offering, which notice shall specify the total number of Units being offered and
the price per Unit at which the Partnership is offering Units in such offering.
The Public REIT OP shall have the right (a "Preemptive Right") to acquire up to
20% of the Units sold by the Partnership in any such offering provided that the
Public REIT OP's investment in the Partnership may be for non-managing general
partner interests, if the Public REIT OP so chooses, rather than the Units
offered by the Partnership. In order to exercise its Pre-Emptive Right, the
Public REIT OP must deliver a written notice (an "Exercise Notice") within 30
days after delivery of notice of such offering to the Partnership and the
General Partner, which Exercise Notice must specify the total number of Units
(or equivalent interest) the Public REIT OP wishes to acquire, up to 20% of the
total number of Units (or equivalent interest) issued in such offering. If the
Public REIT OP delivers an Exercise Notice within such 30 day period, then the
Public REIT OP will be obligated to buy, and the Partnership shall be obligated
to sell to the Public REIT OP, that number of Units (or equivalent interest)
specified in the Exercise Notice, up to 20% of the total number of Units (or
equivalent interest) issued in such offering; provided that the Holding
Partnership shall have no obligation to sell any Units to the Public REIT OP if
such offering is cancelled.


<PAGE>
Miscellaneous

                  This letter agreement shall be governed by the laws of the
State of New York. This letter agreement may be signed in multiple counterparts,
which, taken together, shall constitute one and the same agreement.

                  Please indicate your agreement with the foregoing by signing
below.

                           Very Truly Yours,

                           HINES-SUMISEI U.S. CORE OFFICE FUND, L.P.

                                    By:  Hines US Core Office Capital LLC

                                      By:  Hines Interests Limited Partnership

                                         By:  Hines Holdings, Inc.



                                         By:
                                             ---------------------------------
                                             Name:
                                             Title:

AGREED:

HINES US CORE OFFICE CAPITAL LLC

   By:  Hines US Core Office Capital LLC

     By:  Hines Interests Limited Partnership

       By:  Hines Holdings, Inc.



       By:
           -----------------------------------
           Name:
           Title:


<PAGE>

Hines US CORE OFFICE CAPITAL ASSOCIATES II LIMITED PARTNERSHIP

   By:  Hines US Core Office Capital LLC

     By:  Hines Interests Limited Partnership

       By:  Hines Holdings, Inc.



        By:
           ---------------------------------------------------
            Name:
            Title:

HINES REIT PROPERTIES, L.P.

   By:  Hines Real Estate Investment Trust, Inc.


        By:
           ---------------------------------------------------
            Name:
            Title: