<PAGE>

                                                       Exhibit 4.3

<TABLE>
<CAPTION>
<S>              <C>                                                                 <C>
   NUMBER                       (SEE REVERSE LEGEND)                                   WARRANTS
_________-     (THIS WARRANT WILL BE VOID IF NOT EXERCISED PRIOR TO 5:00 P.M.
                            NEW YORK CITY TIME, __________, 2008

                     TREMISIS ENERGY ACQUISITION CORPORATION
                                                                                                       CUSIP _______________
                                                                           WARRANT
</TABLE>

THIS CERTIFIES THAT, for value received


is the registered holder of a Warrant or Warrants expiring ________, 2008 (the
"Warrant") to purchase one fully paid and non-assessable share of Common Stock,
par value $.0001 per share ("Shares"), of Tremisis Energy Acquisition
Corporation, a Delaware corporation (the "Company"), for each Warrant evidenced
by this Warrant Certificate. The Warrant entitles the holder thereof to purchase
from the Company, commencing on the later of (i) the consummation by the Company
of a merger, capital stock exchange, asset acquisition or other similar business
combination or (ii) __________, 2005, such number of Shares of the Company at
the price of $5.00 per share, upon surrender of this Warrant Certificate and
payment of the Warrant Price at the office or agency of the Warrant Agent,
American Stock Transfer & Trust Company (such payment to be made by check made
payable to the Warrant Agent), but only subject to the conditions set forth
herein and in the Warrant Agreement between the Company and American Stock
Transfer & Trust Company. The Warrant Agreement provides that upon the
occurrence of certain events the Warrant Price and the number of Warrant Shares
purchasable hereunder, set forth on the face hereof, may, subject to certain
conditions, be adjusted. The term Warrant Price as used in this Warrant
Certificate refers to the price per Share at which Shares may be purchased at
the time the Warrant is exercised.

     No fraction of a Share will be issued upon any exercise of a Warrant. If
the holder of a Warrant would be entitled to receive a fraction of a Share upon
any exercise of a Warrant, the Company shall, upon such exercise, round up to
the nearest whole number the number of Shares to be issued to such holder.

     Upon any exercise of the Warrant for less than the total number of full
Shares provided for herein, there shall be issued to the registered holder
hereof or his assignee a new Warrant Certificate covering the number of Shares
for which the Warrant has not been exercised.

     Warrant Certificates, when surrendered at the office or agency of the
Warrant Agent by the registered holder hereof in person or by attorney duly
authorized in writing, may be exchanged in the manner and subject to the
limitations provided in the Warrant Agreement, but without payment of any
service charge, for another Warrant Certificate or Warrant Certificates of like
tenor and evidencing in the aggregate a like number of Warrants.

     Upon due presentment for registration of transfer of the Warrant
Certificate at the office or agency of the Warrant Agent, a new Warrant
Certificate or Warrant Certificates of like tenor and evidencing in the
aggregate a like number of Warrants shall be issued to the transferee in
exchange for this Warrant Certificate, subject to the limitations provided in
the Warrant Agreement, without charge except for any applicable tax or other
governmental charge.

     The Company and the Warrant Agent may deem and treat the registered holder
as the absolute owner of this Warrant Certificate (notwithstanding any notation
of ownership or other writing hereon made by anyone), for the purpose of any
exercise hereof, of any distribution to the registered holder, and for all other
purposes, and neither the Company nor the Warrant Agent shall be affected by any
notice to the contrary.

     This Warrant does not entitle the registered holder to any of the rights of
a stockholder of the Company.

     The Company reserves the right to call the Warrant, at any time prior to
its exercise, with a notice of call in writing to the holders of record of the
Warrant, giving 30 days' notice of such call at any time after the Warrant
becomes exercisable if the last sale price of the Shares has been at least $8.50
per share on each of 20 trading days within any 30 trading day period ending on
the third business day prior to the date on which notice of such call is given.
The call price of the Warrants is to be $.01 per Warrant. Any Warrant either not
exercised or tendered back to the Company by the end of the date specified in
the notice of call shall be canceled on the books of the Company and have no
further value except for the $.01 call price.

By

---------------------------------        ---------------------------------------
                        Secretary        Chairman of the Board


<PAGE>



                                SUBSCRIPTION FORM
      To Be Executed by the Registered Holder in Order to Exercise Warrants

The undersigned Registered Holder irrevocably elects to exercise ______________
Warrants represented by this Warrant Certificate, and to purchase the shares of
Common Stock issuable upon the exercise of such Warrants, and requests that
Certificates for such shares shall be issued in the name of


_______________________________________________________________________________
                     (PLEASE TYPE OR PRINT NAME AND ADDRESS)
_______________________________________________________________________________

_______________________________________________________________________________

_______________________________________________________________________________
                 (SOCIAL SECURITY OR TAX IDENTIFICATION NUMBER)

and be delivered to ___________________________________________________________
                     (PLEASE PRINT OR TYPE NAME AND ADDRESS)

_______________________________________________________________________________
and, if such number of Warrants shall not be all the Warrants evidenced by this
Warrant Certificate, that a new Warrant Certificate for the balance of such
Warrants be registered in the name of, and delivered to, the Registered Holder
at the address stated below:

Dated: _____________________            ________________________________________
                                        (SIGNATURE)
                                        ________________________________________
                                        (ADDRESS)
                                        ________________________________________

                                        ________________________________________
                                        (TAX IDENTIFICATION NUMBER)

                                   ASSIGNMENT
       To Be Executed by the Registered Holder in Order to Assign Warrants

For Value Received, _______________________ hereby sell, assign, and transfer
unto

_______________________________________________________________________________
                     (PLEASE TYPE OR PRINT NAME AND ADDRESS)
_______________________________________________________________________________

_______________________________________________________________________________

_______________________________________________________________________________
                 (SOCIAL SECURITY OR TAX IDENTIFICATION NUMBER)

and be delivered to ___________________________________________________________
                     (PLEASE PRINT OR TYPE NAME AND ADDRESS)

______________________ of the Warrants represented by this Warrant Certificate,
and hereby irrevocably constitute and appoint _________________________________
Attorney to transfer this Warrant Certificate on the books of the Company, with
full power of substitution in the premises.

Dated: _________________________               _________________________________
                                               (SIGNATURE)

THE SIGNATURE TO THE ASSIGNMENT OF THE SUBSCRIPTION FORM MUST CORRESPOND TO THE
NAME WRITTEN UPON THE FACE OF THIS WARRANT CERTIFICATE IN EVERY PARTICULAR,
WITHOUT ALTERATION OR ENLARGEMENT OR ANY CHANGE WHATSOEVER, AND MUST BE
GUARANTEED BY A COMMERCIAL BANK OR TRUST COMPANY OR A MEMBER FIRM OF THE
AMERICAN STOCK EXCHANGE, NEW YORK STOCK EXCHANGE, PACIFIC STOCK EXCHANGE OR
CHICAGO STOCK EXCHANGE.