November
      1, 2007

     

    Tremisis
      Energy Acquisition Corporation II

    11622
      Monica Street

    Houston,
      Texas 77024

    


    Merrill
      Lynch, Pierce, Fenner & Smith Incorporated

    4
      World
      Financial Center

    250
      Vesey
      Street

    New
      York,
      New York 10080

    


    EarlyBirdCapital,
      Inc.

    275
      Madison Avenue

    Suite
      1203

    New
      York,
      New York 10016

    


    
      	 	 	
              Re:

            	
              Initial
                Public Offering

            


    

    


    Gentlemen:

    


    The
      undersigned stockholder, officer and director of Tremisis Energy Acquisition
      Corporation II (“Company”), in consideration of Merrill Lynch, Pierce, Fenner
& Smith Incorporated and EarlyBirdCapital, Inc. (collectively, the
“Underwriters”) entering into a letter of intent (“Letter of Intent”) to
      underwrite an initial public offering of the securities of the Company (“IPO”)
      and embarking on the IPO process, hereby agrees as follows (certain capitalized
      terms used herein are defined in paragraph 15 hereof):

    


    1. If
      the
      Company solicits approval of its stockholders of a Business Combination, the
      undersigned will vote all Insider Shares owned by him in accordance with the
      majority of the votes cast by the holders of the IPO Shares. 

    


    2. In
      the
      event that the Company fails to consummate a Business Combination within 24
      months from the effective date (“Effective Date”) of the registration statement
      relating to the IPO, the undersigned will (i) cause the Trust Fund (as defined
      in the Letter of Intent) to be liquidated and distributed to the holders of
      IPO
      Shares and (ii) take all reasonable actions within his power to cause the
      Company to liquidate as soon as reasonably practicable. The undersigned hereby
      waives any and all right, title, interest or claim of any kind in or to any
      distribution of the Trust Fund and any remaining net assets of the Company
      as a
      result of such liquidation with respect to his Insider Shares (“Claim”) and
      hereby waives any Claim the undersigned may have in the future as a result
      of,
      or arising out of, any contracts or agreements with the Company and will not
      seek recourse against the Trust Fund for any reason whatsoever. In the event
      of
      the liquidation of the Trust Fund, the undersigned agrees to indemnify and
      hold
      harmless the Company against any and all loss, liability, claims, damage and
      expense whatsoever (including, but not limited to, any and all legal or other
      expenses reasonably incurred in investigating, preparing or defending against
      any litigation, whether pending or threatened, or any claim whatsoever) which
      the Company may become subject as a result of any claim by any vendor or other
      person who is owed money by the Company for services rendered or products sold
      or contracted for, or by any target business, but only to the extent necessary
      to ensure that such loss, liability, claim, damage or expense does not reduce
      the amount in the Trust Fund.

     

    
      
        
        

      

      
        
        

        
          

        

      

      
        
        

      

    

     

    
      Tremisis
        Energy Acquisition Corporation II

      Merrill
        Lynch, Pierce, Fenner & Smith
        Incorporated

      EarlyBirdCapital,
        Inc.

      November
        1, 2007

      Page
        2


    

    3. In
      order
      to minimize potential conflicts of interest which may arise from multiple
      affiliations, the undersigned agrees to present to the Company for its
      consideration, prior to presentation to any other person or entity, any suitable
      opportunity to acquire an operating business, until the earlier of the
      consummation by the Company of a Business Combination, the liquidation of the
      Company or until such time as the undersigned ceases to be an officer or
      director of the Company, subject to any pre-existing fiduciary and contractual
      obligations the undersigned might have.

    


    4. The
      undersigned acknowledges and agrees that the Company will not consummate any
      Business Combination which involves a company which is affiliated with any
      of
      the Insiders unless
      the Company obtains an opinion from an independent investment banking firm
      reasonably acceptable to the Underwriters that the business combination is
      fair
      to the Company’s stockholders from a financial perspective.

     

    5. Neither
      the undersigned, any member of the family of the undersigned, nor any affiliate
      (“Affiliate”) of the undersigned will be entitled to receive and will not accept
      any compensation for services rendered to the Company prior to or in connection
      with the consummation of the Business Combination; provided that the undersigned
      shall be entitled to reimbursement from the Company for his out-of-pocket
      expenses incurred in connection with seeking and consummating a Business
      Combination.  

     

    6. Neither
      the undersigned, any member of the family of the undersigned, nor any Affiliate
      of the undersigned will be entitled to receive or accept a finder’s fee or any
      other compensation in the event the undersigned, any member of the family of
      the
      undersigned or any Affiliate of the undersigned originates a Business
      Combination. 

     

    
      
        
        

      

      
        
        

        
          

        

      

      
        
        

      

    

     

    
      Tremisis
        Energy Acquisition Corporation II

      Merrill
        Lynch, Pierce, Fenner & Smith
        Incorporated

      EarlyBirdCapital,
        Inc.

      November
        1, 2007

      Page
        3

       

    

    7. The
      undersigned will escrow all of his Insider Shares acquired prior to the IPO
      until one year after the consummation by the Company of a Business Combination
      subject to the terms of a Stock Escrow Agreement which the Company will enter
      into with the undersigned and an escrow agent acceptable to the
      Company.

    


    8. The
      undersigned agrees to be the Chairman of the Board, Chief Executive Officer,
      Chief Financial Officer and Secretary of
      the
      Company until the earlier of the consummation by the Company of a Business
      Combination or the liquidation of the Company. The undersigned’s biographical
      information furnished to the Company and the Underwriters and attached hereto
      as
      Exhibit A is true and accurate in all respects, does not omit any material
      information with respect to the undersigned’s background and contains all of the
      information required to be disclosed pursuant to Item 401 of Regulation S-K,
      promulgated under the Securities Act of 1933. The undersigned’s Questionnaire
      furnished to the Company and the Underwriters and annexed as Exhibit B
      hereto is true and accurate in all respects. The undersigned represents and
      warrants that:

    


    (a) he
      is not
      subject to, or a respondent in, any legal action for, any injunction,
      cease-and-desist order or order or stipulation to desist or refrain from any
      act
      or practice relating to the offering of securities in any
      jurisdiction;

    


    (b) he
      has
      never been convicted of or pleaded guilty to any crime (i) involving any fraud
      or (ii) relating to any financial transaction or handling of funds of another
      person, or (iii) pertaining to any dealings in any securities and he is not
      currently a defendant in any such criminal proceeding; and

    


    (c) he
      has
      never been suspended or expelled from membership in any securities or
      commodities exchange or association or had a securities or commodities license
      or registration denied, suspended or revoked.

    


    9. The
      undersigned has full right and power, without violating any agreement by which
      he is bound, to enter into this letter agreement and to serve as Chairman of
      the
      Board, Chief Executive Officer, Chief Financial Officer and Secretary of the
      Company.

    


    10. The
      undersigned hereby waives his right to exercise conversion rights with respect
      to any shares of the Company’s common stock owned or to be owned by the
      undersigned, directly or indirectly, and agrees that he will not seek conversion
      with respect to such shares in connection with any vote to approve a Business
      Combination.

     

    
      
        
        

      

      
        
        

        
          

        

      

      
        
        

      

    

    
       

      Tremisis
        Energy Acquisition Corporation II

      Merrill
        Lynch, Pierce, Fenner & Smith
        Incorporated

      EarlyBirdCapital,
        Inc.

      November
        1, 2007

      Page
        4

       

    

    11. The
      undersigned hereby agrees to not propose, or vote in favor of, an amendment
      to
      the Company’s Certificate of Incorporation to extend the period of time in which
      the Company must consummate a Business Combination prior to its liquidation.
      Should such a proposal be put before stockholders other than through actions
      by
      the undersigned, the undersigned hereby agrees to vote against such proposal.
      This paragraph may not be modified or amended under any
      circumstances.

    


    12. In
      the
      event that the Company does not consummate a Business Combination and must
      liquidate and its remaining net assets are insufficient to complete such
      liquidation, the undersigned agrees to advance such funds necessary to complete
      such liquidation and agrees not to seek repayment for such
      expenses.

    


    13. The
      undersigned authorizes any employer, financial institution, or consumer credit
      reporting agency to release to the Underwriters and their legal representatives
      or agents (including any investigative search firm retained by the Underwriters)
      any information they may have about the undersigned’s background and finances
      (“Information”). Neither the Underwriters nor their agents shall be violating
      the undersigned’s right of privacy in any manner in requesting and obtaining the
      Information and the undersigned hereby releases them from liability for any
      damage whatsoever in that connection.

    


    14. This
      letter agreement shall be governed by and construed and enforced in accordance
      with the laws of the State of New York, without
      giving effect to conflicts of law principles that would result in the
      application of the substantive laws of another jurisdiction.
      The
      undersigned hereby (i) agrees that any action, proceeding or claim against
      him
      arising out of or relating in any way to this letter agreement (a “Proceeding”)
      shall be brought and enforced in the courts of the State of New York of the
      United States of America for the Southern District of New York, and irrevocably
      submits to such jurisdiction, which jurisdiction shall be exclusive, (ii) waives
      any objection to such exclusive jurisdiction and that such courts represent
      an
      inconvenient forum and (iii) irrevocably agrees to appoint Graubard Miller
      as
      agent for the service of process in the State of New York to receive, for the
      undersigned and on his behalf, service of process in any Proceeding. If for
      any
      reason such agent is unable to act as such, the undersigned will promptly notify
      the Company and the Underwriters and appoint a substitute agent acceptable
      to
      each of the Company and the Underwriters within 30 days and nothing in this
      letter will affect the right of either party to serve process in any other
      manner permitted by law.  

     

    
      
        
        

      

      
        
        

        
          

        

      

      
        
        

      

    

    
      Tremisis
        Energy Acquisition Corporation II

      Merrill
        Lynch, Pierce, Fenner & Smith
        Incorporated

      EarlyBirdCapital,
        Inc.

      November
        1, 2007

      Page
        5

       

    

    15. As
      used
      herein, (i) a “Business Combination” shall mean an acquisition by merger,
      capital stock exchange, asset or stock acquisition, reorganization or otherwise,
      of an operating business; (ii) “Insiders” shall mean all officers, directors and
      stockholders of the Company immediately prior to the IPO; (iii) “Insider Shares”
shall mean all of the shares of Common Stock of the Company acquired by an
      Insider prior to the IPO; and (iv) “IPO Shares” shall mean the shares of Common
      Stock issued in the Company’s IPO.

     

    
      	 	 	 
	 	 	
              Lawrence
                S. Coben

            
	 	 	
              Print
                Name of Insider

            
	
            	
            	
               

               

            
	 	 	
              /s/ Lawrence
                S. Coben

            
	 	
              

              Signature