




                                  June 27, 2006



VIA EDGAR and FAX
- -----------------

John Cash, Branch Chief
Division of Corporation Finance
United States Securities and Exchange Commission
100 F Street, N.E.
Washington, D.C. 20549-7010


     Re:  ADA-ES, Inc.
          Form 10-K for the year ended December 31, 2005
          Form 10-Q for the period ended March 31, 2006
          File No. 0-50216
          ----------------

Dear Mr. Cash:

     On behalf of ADA-ES, Inc. ("we" or the "Company"), we respond as follows to
the Staff's comment letter dated June 22, 2006 relating to the above-captioned
filings on Forms 10-K and 10-Q. Please note that for the Staff's convenience, we
have recited each of the Staff's comments and provided the Company's response to
each immediately thereafter.


     Form 10-KSB for the fiscal year ended December 31, 2005
     -------------------------------------------------------

     Item 6. Management's Discussion and Analysis
     --------------------------------------------
             Liquidity and Capital Resources page 15
             ---------------------------------------

          1.   We note your analysis of cash flows on page 16. Please revise
               your analysis of operating cash flows in future filings to
               address the significant line items seen on your cash flow
               statement and provide your readers with insight into the
               underlying reasons for those changes. For example, it appears
               that your accounts receivable and accounts payable both increased
               significantly in 2005, but you have not explained the reasons for
               these changes. Furthermore, since your accounts receivable
               turnover appears to have decreased from 2004 to 2005, the
               increase in your accounts receivable appears to be attributable
               to more than simply a higher level of annual revenues. Refer to
               Item 303(b) of Regulation S-X and our Release 33-8350, available
               on our website at www.sec.gov/rules/interp/33-8350.htm.

     We note the Staff's comment regarding our analysis of cash flows and, as
     requested, we will revise our analysis of operating cash flow in future
     filings to address the significant line items shown on our cash flow
     statement. Such analysis will be expanded to provide the readers with
     further insight into the underlying reasons for the noted changes.

             Results of Operations page 16
             -----------------------------

          2.   We note that you are analyzing revenues on a segmental basis and
               analyzing all other income statement line items on a consolidated
               basis. Please revise future filings to analyze your segmental
               measure of profit or loss, or the individual line items
               comprising this measure, on a segmental basis. Refer to our
               Release 33-8350.

<PAGE>

John Cash, Branch Chief
Securities & Exchange Commission
June 27, 2006
Page 2



     We note the Staff's comment regarding our analysis of non-revenue income
     statement items on a consolidated basis. As requested, we will revise our
     analysis of such items in future filings to address the segmental measure
     of profit or loss, and/or the individual line items comprising that measure
     on a segmental basis.


             Item 8A Controls and Procedures, page 19
             ----------------------------------------

          3.   We note your disclosure that your "Chief Executive and Financial
               Officers believe that these controls and procedures are effective
               to ensure that [you are] able to record, process, summarize and
               disclose the information [you are] required to disclosure in the
               reports [you file] with the SEC within the required time
               periods." Please confirm to us, and revise future filings to
               clarify, if true, that your officers concluded that your
               disclosure controls and procedure are also effective to ensure
               that information required to be disclosed in the reports that you
               file or submit under the Exchange Act is accumulated and
               communicated to your management, including your chief executive
               officer and chief financial officer, to allow timely decisions
               regarding required disclosure. See Exchange Act Rule 13a-15(e).
               Alternatively, you may revise future filings to simply state that
               your disclosure controls and procedures are effective or
               ineffective without providing the definitions.


     We hereby confirm to you that our officers concluded that our disclosure
     controls and procedures are also effective to ensure that information
     required to be disclosed in the reports that we file or submit under the
     Exchange Act is accumulated and communicated to our management, including
     our chief executive officer and chief financial officer, to allow timely
     decisions regarding required disclosure. We also confirm that we will
     either revise future filings to clarify this point or to simply state that
     our disclosure controls and procedures are effective or ineffective without
     providing the definitions.

             Note 1 - Summary of Nature of Operations and Significant Accounting
             Policies Nature of Operations, page F-7
             -------------------------------------------------------------------


          4.   Based on your disclosures on pages five and 14, we assume that
               you have a joint venture with Arch Coal. If our assumption is
               correct, please tell us how you account for your investment in
               this joint venture. If our assumption is incorrect, please
               explain this matter to us in more detail. Revise future filings
               to clarify this matter.

     Although we have entered into an agreement with Arch Coal that provides for
     the formation of a JV to market and sell certain of our products, those JV
     activities have thus far been immaterial. Other than an assignment of
     license rights to the JV, we have made no other investment. The JV
     agreement contemplated the acquisition and operation of equipment, and the
     potential for the purchase, treatment and sale of coal. None of those
     activities have taken place nor does it now appear likely that such
     activities will ever be significant. The JV owns no assets and has no
     liabilities. We have accounted for payments received from Arch as revenue
     and have recorded 100% of all costs related to such activities. We will
     revise future filings to note that JV activities to date have been
     immaterial and that the JV owns no equipment and has no outstanding
     liabilities.

<PAGE>

John Cash, Branch Chief
Securities & Exchange Commission
June 27, 2006
Page 3



             Revenue Recognition, page F-8
             -----------------------------

          5.   We read that you use percentage of completion accounting for all
               significant contracts excluding government contracts and chemical
               sales. We also read that you recognize revenue on government
               contracts based on the time and expenses incurred to date. We
               have the following comments:

               o    Please provide us with a more detailed description of these
                    significant contracts for which you use percentage of
                    completion accounting, and tell us how you determined that
                    this methodology was appropriate.
               o    Please explain to us in more detail how you account for
                    revenues on government contracts, and tell us how you
                    determined that this methodology was appropriate.
               o    Please tell us how you account for your commercial mercury
                    emissions control contracts. In this regard, we note your
                    statement on page 4 that these contracts have delivery
                    milestones. If you have any other contracts that have
                    deliverables, please tell us how you account for those
                    contracts.
               o    Please tell us if any of your contracts are for the
                    performance of services. If so, please explain to us how you
                    account for those revenues. If you use the percentage of
                    completion method, please tell us how you determined that
                    this methodology was appropriate. Refer to Section 2(F)(2)
                    of our outline of Current Accounting and Disclosure Issues,
                    available on our website at
                    www.sec.gov/divisions/corpfin/acctdis120105.pdf.
               o    Please tell us how you account for revenues from your
                    Combustion Additives segment, including those generated by
                    the JV with Arch Coal and any other revenues.

     A.   Detailed description of significant contracts for which we use
          percentage of completion accounting - The significant contracts for
          which we use percentage of completion accounting for revenue
          recognition represent fixed price contracts for the supply of
          Activated Carbon Injections (ACI) systems and fixed price contracts
          for commercial mercury emission measurement and consulting services.
          The ACI contracts may cover a period from 6 months to over a year and
          the consulting contracts may span a period of several months. We have
          determined that percentage of completion accounting provides the best
          measure of periodic income results since we have available evidence of
          the ultimate proceeds from the fixed price nature of the contracts
          (APB Statement 4, Paragraph 152). In addition, our estimates of costs
          to complete and extent of progress toward completion are reasonably
          dependable, which therefore makes percentage of completion accounting
          preferable over the completed contract method (ARB No. 45, paragraph
          15).

<PAGE>

John Cash, Branch Chief
Securities & Exchange Commission
June 27, 2006
Page 4



     B.   Accounting for revenues on government contracts - Revenue on our
          government contracts is recognized as costs (time, materials and
          burden rates) are incurred. In this case we believe that both the
          earnings process is complete and an exchange has taken place so that
          revenue recognition on that basis is appropriate (APB Statement 4,
          Paragraph 150). These contracts specifically allow us to invoice and
          collect amounts from the DOE as we incur costs.

     C.   Accounting for commercial mercury emission control contracts - These
          contracts may be either fixed price or time and materials based, and
          may be for ACI systems or for services. In the case of fixed price
          contracts, revenues is recognized as noted in A. above using
          percentage of completion accounting. For such contracts that are based
          on time and materials, revenue is recognized as costs are incurred as
          in B. above. In every case where there are delivery milestones, such
          milestones determine when we can contractually invoice the customer
          some proportion of the fixed price amount. The delivery milestones are
          typically very close to percentage complete such that revenue is
          usually not too far ahead or behind of invoicing.

     D.   Contracts for the performance of services - Several of our contracts
          are for the performance of services. The description of these
          contracts and our revenue accounting is described above.

     E.   Revenues for Combustion Aids segment - Revenues in the Combustion Aids
          segment are primarily generated from chemical sales, which are
          accounted for in the same manner as our other chemical sales described
          in Revenue Recognition on F-8 of our Consolidated Financial
          Statements. Revenue on such chemical sales is recognized when products
          are shipped to customers. A reserve, if any is required, is
          established for any returns, based on historical trends. Chemical
          products are shipped FOB shipping point and title passes to the
          customer when the chemicals are shipped. Our sales agreements do not
          contain a right of inspection or acceptance provision and products are
          generally received by customers within one day of shipment. We have
          had no significant history of non-acceptance, nor of replacing goods
          damaged or lost in transit. A minor amount of consulting revenue in
          this segment is recognized as services are performed and collection is
          assured. With regard to the JV with Arch Coal, amounts received from
          Arch to reimburse us for costs are recognized as revenue, and we
          credit Arch a per ton amount on product sold. Amounts received from
          and credited to Arch Coal in 2005 under the JV were immaterial.

             Goodwill, page F-9
             ------------------

          6.   We note your reference to the investment banking firm that
               performed a valuation of your company. In future filings either
               name these experts or delete your reference to them. We remind
               you that if you refer to and identify these experts, you must
               include their consents when the reference is included in a filing
               in the 1933 Act environment. Refer to Section 436(b) of
               Regulation C.

<PAGE>

John Cash, Branch Chief
Securities & Exchange Commission
June 27, 2006
Page 5



     We note the Staff comment and will remove the reference to the investment
     banking firm in future filings.


          7.   We read that based upon the 2002 valuation of your company, which
               was updated in subsequent years, you determined that no
               impairment of your goodwill was required. Please explain to us in
               more detail how you determined that your goodwill was not
               impaired. We remind you that goodwill impairment must be tested
               at the "reporting unit" level, as that term is defined in SFAS
               142, and not at the level of your consolidated company. If you
               have tested goodwill at the reporting unit level, please revise
               your disclosure in future filings to clarify this matter.

     The unamortized balance of goodwill carried on our financial statements
     arose as the result of acquiring the Flue Gas Conditioning (FGC) business
     and intellectual property of ADA Environmental Solutions. The testing to
     determine that our goodwill was not impaired was performed on the reporting
     unit level of our FGC product line, by calculating future expected net cash
     flows from that reporting unit. Those cash flows were of an amount
     sufficient to support the carrying value of the goodwill as reported on the
     financial statements. We will revise our disclosure in future filings to
     clarify that we have tested goodwill at the reporting unit level.

             Note 3 - Investments, page F-13
             -------------------------------


          8.   Please reconcile for us the amount you have disclosed in note
               three regarding your unrealized gain/loss on investments to the
               amount you have shown in comprehensive income for "unrealized
               gains and losses on certain investments in debt and equity
               securities, net of tax."

     The reconciliation of unrealized gain/loss on investments to the amount we
     have shown in comprehensive income for unrealized gains and losses on
     certain investments in debt and equity securities at December 31, 2005 is
     as follows:

       Gross Unrealized Gain, as per FN3                       $ 146,000
       Gross unrealized Loss, as per FN3                         (94,000)
                                                               ---------
                Net Unrealized Gain                            $  52,000
       Estimated tax provision @ 37.5%                           (19,000)
                                                               ---------
       Accumulated other comprehensive income @ 12/31/05       $  33,000
       Accumulated other comprehensive income @ 12/31/04       $ (34,000)
                                                               ---------
       Unrealized gains and losses on certain Investments in
         Debt and Equity Securities, net of tax                $  (1,000)
                                                               =========

<PAGE>

John Cash, Branch Chief
Securities & Exchange Commission
June 27, 2006
Page 6



             Note 6 - Commitments and Contingencies, page F-17
             -------------------------------------------------

          9.   We note your discussion, here and on page ten, of your
               performance guarantees. Please tell us how you have accounted for
               these performance guarantees and, if these are effectively
               warranties of your equipment, what consideration you have given
               to providing the warranty disclosures as indicated in paragraph
               14 of FIN 45. Quantify for us, and disclose in future filings if
               material, the amount, if any, that you have paid under such
               performance guarantees to date.


     Our performance guarantees are related to performance of non-financial
     assets that are owned by the guaranteed party and are thus not subject to
     the initial recognition and initial measurement provisions of FIN 45 per
     paragraph 7b. We have considered the disclosures indicated by paragraph 14
     of FIN 45 but as of December 31, 2005 such amounts were immaterial. We
     recorded our first accrued liability for performance guarantees in the
     fourth quarter of 2005 corresponding to our first commercial sale, and so
     the beginning balance would be zero. There were no reductions to that
     liability as no payments were made, and the accrual for guarantees issued
     during the period along with the ending balance amounted to $21,000.

             Note 10 - Business Segment Information, page F- 19
             --------------------------------------------------


          10.  In future filings please provide a brief description of the
               non-allocated general and administrative expenses. Refer to
               paragraphs 31-32 of SFAS 131.


     We note the Staff's comment and will include a brief description of the
     non-allocated general and administrative expenses on our business segment
     information.

             Form 10-Q for the period ended March 31, 2006
             ---------------------------------------------

             Item 2. Management's Discussion and Analysis - Overview
             -------------------------------------------------------


          11.  We read that you have deferred $312,000 of costs related to your
               M&A activities in other long-term assets. Please describe these
               deferred costs to us, and tell us how you determined that it was
               appropriate to capitalize these costs. We remind you that only
               the direct costs of a business combination may be capitalized.
               Refer to paragraph 24 of SFAS 141.


The deferred costs related to our M&A activities consist of third-party legal
fees incurred in due diligence and agreement drafting, an initial payment to a
third-party for an expected fairness opinion to be issued to our Board of
Directors and other out-of-pocket costs incurred in the ongoing due diligence
process. We determined that it was proper to defer and capitalize these costs at
March 31, 2006 due to the status of the effort at that time and nature of the
costs incurred. We consider such costs direct costs of the potential business
combination, which would be included in the cost of an entity acquired in a
business combination. In early March 2006 we entered into a non-binding letter
of intent to acquire a certain international business and began the due
diligence process shortly thereafter, which process was ongoing as of March 31,
2006 and through the date of filing our Form 10-Q.

<PAGE>
John Cash, Branch Chief
Securities & Exchange Commission
June 27, 2006
Page 7



             Item 3. Controls and Procedures
             -------------------------------


          12.  We read that your "Chief Executive and Financial Officers believe
               that these controls and procedures are effective to ensure that
               [you are] able to collect, process and disclose the information
               [you are] required to disclosure in the reports [you file] with
               the SEC within the required time periods." This appears to be an
               abbreviated definition of effective controls and procedures as
               defined in Exchange Act Rule 13a-15(e). Please confirm to us, and
               revise future filings to clarify, if true, that your officers
               concluded that your disclosure controls and procedures are
               effective to ensure that you are able to record, process,
               summarize and disclose the information you are required to
               disclosure in the reports you file with the SEC within the
               required time periods and your disclosure controls and procedure
               are effective to ensure that information required to be disclosed
               in the reports that you file or submit under the Exchange Act is
               accumulated and communicated to your management, including your
               chief executive officer and chief financial officer, to allow
               timely decisions regarding required disclosure. Alternatively,
               you may revise future filings to simply state that your
               disclosure controls and procedures are effective or ineffective
               without providing the definitions.

     We hereby confirm to you that our officers concluded that our disclosure
     controls and procedures are effective to ensure that we are able to record,
     process, summarize and disclose the information we are required to
     disclosure in the reports we file with the SEC within the required time
     periods and that our disclosure controls and procedures are effective to
     ensure that information required to be disclosed in the reports that we
     file or submit under the Exchange Act is accumulated and communicated to
     our management, including our chief executive officer and chief financial
     officer, to allow timely decisions regarding required disclosure. We also
     confirm that we will either revise future filings to clarify these points
     or to simply state that our disclosure controls and procedures are
     effective or ineffective without providing the definitions.

     Acknowledging Statement
     -----------------------

     ADA-ES, Inc. hereby acknowledges that:
          o    It is responsible for the adequacy and accuracy of the
               disclosures in its filings;
          o    Staff comments or changes to disclosure in response to Staff
               comments do not foreclose the Commission from taking any action
               with respect to the noted filings; and
          o    It may not assert Staff comments as a defense in any proceeding
               initiated by the Commission or any person under the federal
               securities laws of the United States.

<PAGE>

John Cash, Branch Chief
Securities & Exchange Commission
June 27, 2006
Page 8



     I believe that this responds to all of the Staff's comments and as
presented there is no amendment to any current filing required. Please do not
hesitate to contact me if you have any further questions of comments. I can be
reached at telephone 303-734-1727.


                                           Sincerely,

                                           ADA-ES, Inc.

                                           /s/ Mark H. McKinnies


                                           Mark McKinnies
                                           Senior VP and Chief Financial Officer





