Exhibit 10.54

ASSIGNMENT AND ASSUMPTION OF PURCHASE AGREEMENT

This Assignment and Assumption of Purchase
Agreement (Assignment) is entered into between KBS CAPITAL ADVISORS LLC, a Delaware limited liability company (Assignor) and KBS SOUTH TOWNE, LLC, a Delaware limited liability company (Assignee), as of
October 9, 2007 (Effective Date).

RECITALS

A. Pursuant to the terms of that certain Purchase Agreement for Real Property and Escrow Instructions dated as of September 10, 2007, by and between
WORKERS COMPENSATION FUND, a Utah corporation, formerly known as Workers Compensation Fund of Utah, as seller, and Assignor, as buyer (the Purchase Agreement), Assignor agreed to acquire the Property (as such term is defined in the
Purchase Agreement) commonly referred to as South Towne Corporate Center Phases I and II.

B. Assignor desires to assign, without recourse,
representation or warranty, all of its rights, benefits, liabilities and obligations arising under the Purchase Agreement (and related documents) to Assignee, and Assignee desires to assume all of said rights, benefits, liabilities and obligations.

NOW, THEREFORE, in consideration of the foregoing promises, the mutual undertakings of the parties set forth herein and other good and
valuable consideration, the receipt and sufficiency of which are hereby acknowledged by the parties, the parties agree as follows:

1.
Recitals. The above recitals are incorporated herein by reference.

2. Assignment and Assumption. Assignor hereby transfers,
assigns and conveys, without recourse, representation or warranty, express or implied, all of Assignors rights, interests, liabilities and obligations in and to the Property, and all of Assignors rights, interests, liabilities and
obligations under the Purchase Agreement (and related documents) to acquire same to Assignee. Assignee hereby assumes all such rights, interests, liabilities and obligations, and joins in all representations, warranties, releases, and indemnities,
of Assignor under the Purchase Agreement (and related documents) relating to such Property and the Purchase Agreement (and related documents) assigned to it above.

3. Successors and Assigns. This Assignment shall be binding upon and inure to the benefit of the parties successors and assigns.

4. Attorneys Fees. In the event any party institutes any action or proceeding against the other party with regard to this Assignment, the
prevailing party of such action shall be entitled to recover from the nonprevailing party (in addition to all other remedies provided by law) its attorneys fees and costs incurred in such action or proceeding.

5. Release Under Purchase Agreement. Upon consummation of the transactions contemplated by the Purchase Agreement, Assignor shall be automatically
released from its obligations under the Purchase Agreement.

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6. Counterparts. This Assignment may be executed in any number of counterparts, each of which
shall be deemed an original, but all of which when taken together shall constitute one and the same instrument. Each counterpart may be delivered by facsimile transmission. The signature page of any counterpart may be detached therefrom without
impairing the legal effect of the signature(s) thereon provided such signature page is attached to any other counterpart identical thereto.

Executed as of
the date set forth above.

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|                                                              |  |                              
|------------------------------------------------------------- |  | -----------------------------
|ASSIGNOR:                                                    
|                                                             
|KBS CAPITAL ADVISORS LLC,a Delaware limited liability company
|                                                              | 
|By:                                                           |  | /s/ Charles J. Schreiber, Jr.
|                                                              |  | Charles J. Schreiber, Jr.    
|                                                              |  | Chief Executive Officer      

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|S-1 |  | SOUTH TOWNE



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|                                     |  |                                       |  |                                       |  |                                 |  |                                         |  |                               |  | 
|------------------------------------ |  | ------------------------------------- |  | ------------------------------------- |  | ------------------------------- |  | --------------------------------------- |  | ----------------------------- |  | 
|ASSIGNEE                             |  |                                      
|                                     | 
|KBS SOUTH TOWNE, LLC,                |  |                                      
|a Delaware limited liability company |  |                                      
|                                     |  |                                      
|By:                                  |  | KBS REIT ACQUISITION XXIX, LLC,       |  |                                      
|                                     |  | a Delaware limited liability company, |  |                                      
|                                     |  | its sole member                       |  |                                      
|                                     |  |                                       | 
|                                     |  | By:                                   |  | KBS REIT PROPERTIES, LLC,             |  |                                
|                                     |  |                                       |  | a Delaware limited liability company, |  |                                
|                                     |  |                                       |  | its sole member                       |  |                                
|                                     |  |                                       |  |                                      
|                                     |  |                                       |  | By:                                   |  | KBS LIMITED PARTNERSHIP,        |  |                                        
|                                     |  |                                       |  |                                       |  | a Delaware limited partnership, |  |                                        
|                                     |  |                                       |  |                                       |  | its sole member                 |  |                                        
|                                     |  |                                       |  |                                       | 
|                                     |  |                                       |  |                                       |  | By:                             |  | KBS REAL ESTATE INVESTMENT TRUST, INC., |  |                              
|                                     |  |                                       |  |                                       |  |                                 |  | a Maryland corporation,                 |  |                              
|                                     |  |                                       |  |                                       |  |                                 |  | general partner                         |  |                              
|                                     |  |                                       |  |                                       |  |                                
|                                     |  |                                       |  |                                       |  |                                 |  | By:                                     |  | /s/ Charles J. Schreiber, Jr. |  | 
|                                     |  |                                       |  |                                       |  |                                 |  |                                         |  | Charles J. Schreiber, Jr.     |  | 
|                                     |  |                                       |  |                                       |  |                                 |  |                                         |  | Chief Executive Officer       |  | 

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|S-2 |  | SOUTH TOWNE