<PAGE>

                                                                     Exhibit 4.2

                             LETTER OF TRANSMITTAL
                        TO TENDER SHARES OF COMMON STOCK
                                       OF
                                   AROC INC.
              PURSUANT TO THE OFFER TO PURCHASE DATED MAY 14, 2001

--------------------------------------------------------------------------------
THE OFFER, AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY
TIME, ON JUNE 12, 2001, UNLESS THE OFFER IS EXTENDED.
--------------------------------------------------------------------------------
                        The Depositary for the Offer is:

                         REGISTRAR AND TRANSFER COMPANY

                                Delivery Address

             By Hand Delivery,
        Overnight Courier or Mail:                   By Facsimile:

       Registrar & Transfer Company                 (908) 497-2311
     Attn: Reorganization Department
           10 Commerce Drive
          Cranford, NJ  07016
            (800) 368-5948

DELIVERY OF THIS LETTER OF TRANSMITTAL TO AN ADDRESS OTHER THAN AS SET FORTH
ABOVE WILL NOT CONSTITUTE A VALID DELIVERY.  DELIVERIES TO THE COMPANY WILL NOT
BE FORWARDED TO THE DEPOSITARY AND THEREFORE WILL NOT CONSTITUTE VALID DELIVERY.

     This Letter of Transmittal is to be used only if certificates are to be
forwarded herewith pursuant to the procedures set forth in of the Offer to
Purchase (as defined below).

<TABLE>
<CAPTION>
                         DESCRIPTION OF SHARES TENDERED (SEE INSTRUCTIONS 3 AND 4)
--------------------------------------------------------------------------------------------------------
<S>                                                  <C>           <C>                  <C>
Name(s) and Address(es) of Registered Holder(s)                        Shares Tendered
(Please fill in exactly as name(s) appear(s) on         (Attach additional signed list if necessary)
 Certificate(s))
--------------------------------------------------------------------------------------------------------
                                                     Certificate    Total Number of     Number of Shares
                                                       Number      Shares Represented     Tendered(1)
                                                                     By Certificate
                                               ---------------------------------------------------------

                                               ---------------------------------------------------------

                                               ---------------------------------------------------------

                                               ---------------------------------------------------------

                                                               Total Shares
--------------------------------------------------------------------------------------------------------
</TABLE>
(1)  Unless otherwise indicated, it will be assumed that all Shares represented
     by each Share certificate delivered to the Depositary are being tendered
     hereby. See Instruction 4.

NOTE: SIGNATURES MUST BE PROVIDED BELOW.  PLEASE READ THE INSTRUCTIONS SET FORTH
IN THIS LETTER OF TRANSMITTAL CAREFULLY.

[ ]  Check here if you cannot locate your certificates and require assistance in
     replacing them. Upon receipt of this Letter of Transmittal, the Depositary
     will contact you directly with replacement instructions.
<PAGE>

LADIES AND GENTLEMEN:

     The undersigned hereby tenders to AROC Inc., a Delaware corporation (the
"Company"), the above-described shares of its common stock, par value $0.001 per
share (the "Shares"), at $0.06 per share (the "Purchase Price"), net to the
seller in cash, upon the terms and subject to the conditions set forth in the
Offer to Purchase, dated May 14, 2001 (the "Offer to Purchase"), receipt of
which is hereby acknowledged, and in this Letter of Transmittal (which, as
amended from time to time, together constitute the "Offer").

     Subject to, and effective upon, acceptance for payment of and payment for
the Shares tendered herewith in accordance with the terms and subject to the
conditions of the Offer (including, if the Offer is extended or amended, the
terms and conditions of any such extension or amendment), the undersigned hereby
sells, assigns and transfers to, or upon the order of, the Company all right,
title and interest in and to all the Shares that are being tendered hereby, and
hereby irrevocably constitutes and appoints the Depositary the true and lawful
agent and attorney-in-fact of the undersigned with respect to such Shares, with
full power of substitution (such power of attorney being deemed to be an
irrevocable power coupled with an interest), to:

          (i)  deliver certificates for such Shares, together with all
     accompanying evidences of transfer and authenticity, to or upon the order
     of the Company upon receipt by the Depositary, as the undersigned's agent,
     of the Purchase Price with respect to such Shares;

         (ii)  present certificates for such Shares for cancellation and
     transfer on the books of the Company; and

         (iii) receive all benefits and otherwise exercise all rights of
     beneficial ownership of such Shares, all in accordance with the terms of
     the Offer.

     The undersigned hereby represents and warrants to the Company that the
undersigned has full power and authority to tender, sell, assign and transfer
the Shares tendered hereby and that, when and to the extent the same are
accepted for payment by the Company, the Company will acquire good, marketable
and unencumbered title thereto, free and clear of all liens, restrictions,
charges, encumbrances, conditional sales agreements or other obligations
relating to the sale or transfer thereof, and the same will not be subject to
any adverse claims.  The undersigned will, upon request, execute and deliver any
additional documents deemed by the Depositary or the Company to be necessary or
desirable to complete the sale, assignment and transfer of the Shares tendered
hereby.

     The undersigned represents and warrants to the Company that the undersigned
has read and agrees to all of the terms of the Offer.  All authority herein
conferred or agreed to be conferred shall not be affected by, and shall survive
the death or incapacity of the undersigned, and any obligation of the
undersigned hereunder shall be binding upon the heirs, personal representatives,
successors and assigns of the undersigned. Except as stated in the Offer, this
tender is irrevocable.

     The undersigned understands that tenders of Shares pursuant to any one of
the procedures described in the Offer to Purchase and in the Instructions will
constitute the undersigned's acceptance of the terms and conditions of the
Offer, including the undersigned's representation and warranty to the Company
that (i) the undersigned has a net long position in the Shares or equivalent
securities being tendered within the meaning of Rule 14e-4 promulgated under the
Securities Exchange Act of 1934, as amended, and (ii) the tender of such

                                       2
<PAGE>

Shares complies with Rule 14e-4.  The Company's acceptance for payment of Shares
tendered pursuant to the Offer will constitute a binding agreement between the
undersigned and the Company upon the terms and subject to the conditions of the
Offer.

     The names and addresses of the registered holders should be printed, if
they are not already printed above, exactly as they appear on the certificates
representing Shares tendered hereby.  The certificate numbers, the number of
Shares represented by such certificates, and the number of Shares that the
undersigned wishes to tender should be indicated in the appropriate boxes on
this Letter of Transmittal.

     The undersigned understands that all Shares validly tendered and not
withdrawn will be purchased at the Purchase Price, net to the seller in cash,
upon the terms and subject to the conditions of the Offer, including the
proration provisions, and that the Company will return all other Shares not
purchased because of proration.

     The undersigned recognizes that, under certain circumstances set forth in
the Offer to Purchase, the Company may terminate or amend the Offer or may
postpone the acceptance for payment of, or the payment for, Shares tendered or
may not be required to purchase any of the Shares tendered hereby or may accept
for payment fewer than all of the Shares tendered hereby.

     Unless otherwise indicated under "Special Payment Instructions," please
issue the check for the Purchase Price of any Shares purchased, and/or return
any Shares not tendered or not purchased, in the name(s) of the undersigned.
Similarly, unless otherwise indicated under "Special Delivery Instructions,"
please mail the check for the Purchase Price of any Shares purchased and/or any
certificates for Shares not tendered or not purchased (and accompanying
documents, as appropriate) to the undersigned at the address shown below the
undersigned's signature(s).  In the event that both "Special Payment
Instructions" and "Special Delivery Instructions" are completed, please issue
the check for the Purchase Price of any Shares purchased and/or return any
Shares not tendered or not purchased in the name(s) of, and mail such check
and/or any certificates to, the person(s) so indicated.  The undersigned
recognizes that the Company has no obligation, pursuant to the "Special Payment
Instructions," to transfer any Shares from the name of the registered holder(s)
thereof if the Company does not accept for payment any of the Shares so
tendered.

     The undersigned understands that acceptance of Shares by the Company for
payment will constitute a binding agreement between the undersigned and the
Company upon the terms and subject to the conditions of the Offer.

                                       3
<PAGE>

                   NOTE:   SIGNATURES MUST BE PROVIDED BELOW

                          SPECIAL PAYMENT INSTRUCTIONS
                        (See Instructions 1, 5, 6 and 7)


<TABLE>
<CAPTION>

<S>                                                                  <C>
         SPECIAL PAYMENT INSTRUCTIONS                                          SPECIAL DELIVERY INSTRUCTIONS
       (See Instructions 1, 5, 6 and 7)                                         (See Instructions 5 and 7)

To be completed ONLY if the check for the aggregate                  To be completed ONLY if the check for the
Purchase Price of Shares purchased and/or certificates               Purchase Price of Shares purchased and/or
for Shares not tendered or not purchased are to be                   certificates for Shares not tendered or not
issued in the name of someone other than the                         purchased are to be mailed to someone other than
undersigned:                                                         the undersigned at an address other than that
                                                                     shown below the undersigned's signature(s).
Issue:   [ ] check and/or  [ ] certificate(s) to:
                                                                     Mail:     [ ] check and/or  [ ] certificate(s) to:

Name:_________________________________________________               Name:________________________________________________
      (Please Print)                                                      (Please Print)
Address:______________________________________________               Address:_____________________________________________

______________________________________________________               ______________________________________________________

______________________________________________________               ______________________________________________________
               (Include Zip Code)                                                    (Include Zip Code)

______________________________________________________               ______________________________________________________
     (Tax Identification or Social Security No.)                            (Tax Identification or Social Security No.)
      (See Substitute Form W-9 Included Herein)

</TABLE>

                                       4
<PAGE>

<TABLE>
<CAPTION>

<S>                                                                    <C>
______________________________________________________________________________________________________________________________
                                                         PLEASE SIGN HERE
                                               (TO BE COMPLETED BY ALL SHAREHOLDERS)
 ____________________________________________________________________________________________________________________________


 ____________________________________________________________________________________________________________________________
                                                    (Signature(s) of Owner(s))

 Dated:________________________________________________________________________________________________________________, 2001

 Name(s):____________________________________________________________________________________________________________________
                                                          (Please Print)

 Capacity (full title):______________________________________________________________________________________________________

 Address:____________________________________________________________________________________________________________________
                                                        (Include Zip Code)

 Area Code and Telephone No.:________________________________________________________________________________________________

 (Must be signed by registered holder(s) exactly as name(s) appear(s) on Share certificate(s) or on a security position listing
 or by a person(s) authorized to become registered holder(s) by certificates and documents transmitted herewith. If signature
 is by a trustee, executor, administrator, guardian, attorney-in-fact, officer of a corporation or other person acting in a
 fiduciary or representative capacity, please set forth full title and see Instruction 5.)

                                                     GUARANTEE OF SIGNATURE(S)
                                                    (See Instruction 1 and 5.)

 Name of Firm:_______________________________________________________________________________________________________________

 Authorized Signature:_______________________________________________________________________________________________________

 Name:_______________________________________________________________________________________________________________________
                                                          (Please Print)

 Title:______________________________________________________________________________________________________________________

 Address:____________________________________________________________________________________________________________________

 ____________________________________________________________________________________________________________________________
                                                        (Include Zip Code)

 Area Code and Telephone No.:________________________________________________________________________________________________

 Dated:________________________________________________________________________________________________________________, 2001

______________________________________________________________________________________________________________________________
</TABLE>

                                       5
<PAGE>

                                  INSTRUCTIONS

             FORMING PART OF THE TERMS AND CONDITIONS OF THE OFFER

     1.   Guarantee of Signatures. Except as otherwise provided below, all
signatures on this Letter of Transmittal must be guaranteed by a firm or other
entity that is a member in good standing of the Security Transfer Agent's
Medallion Program, the New York Stock Exchange Medallion Program or the Stock
Exchange Medallion Program (an "Eligible Institution"), unless (i) this Letter
of Transmittal is signed by the registered holder(s) of the Shares tendered
herewith and such holder(s) have not completed the box entitled "Special Payment
Instructions" or the box entitled "Special Delivery Instructions" on this Letter
of Transmittal, or (ii) such Shares are tendered for the account of an Eligible
Institution. See Instruction 5.

     2.   Delivery of Letter of Transmittal and Share Certificates.  This Letter
of Transmittal is to be used if share certificates are to be forwarded herewith.
Certificates for all physically delivered Shares, as well as a properly
completed and duly executed Letter of Transmittal (or manually signed facsimile
thereof) and any other documents required by this Letter of Transmittal, must be
received by the Depositary at one of its addresses set forth on the front page
of this Letter of Transmittal prior to the Expiration Date.  If certificates are
forwarded to the Depositary in multiple deliveries, a properly completed and
duly executed Letter of Transmittal must accompany each such delivery.

     The method of delivery of all documents, including Share certificates, the
Letter of Transmittal and any other required documents, is at the election and
risk of the tendering stockholder, and the delivery will be deemed made only
when actually received by the Depositary. If delivery is by mail, registered
mail with return receipt requested, properly insured, is recommended. In all
cases, sufficient time should be allowed to ensure timely delivery.

     No alternative or contingent tenders will be accepted. By executing this
Letter of Transmittal (or facsimile thereof), the tendering stockholder waives
any right to receive any notice of the acceptance for payment of the Shares.

     3.   Inadequate Space. If the space provided herein is inadequate, the
certificate numbers and/or the number of Shares should be listed on a separate
signed schedule and attached to this Letter of Transmittal.

     4.   Partial Tenders.  If fewer than all the Shares represented by any
certificate delivered to the Depositary are to be tendered, fill in the number
of Shares that are to be tendered in the box entitled "Number of Shares
Tendered."  In such case, a new certificate for the remainder of the Shares
represented by the old certificate will be sent to the person(s) signing this
Letter of Transmittal, unless otherwise provided in the "Special Payment
Instructions" or "Special Delivery Instructions" boxes on this Letter of
Transmittal, as promptly as practicable following the expiration or termination
of the Offer.  All Shares represented by certificates delivered to the
Depositary will be deemed to have been tendered unless otherwise indicated.

     5.   Signatures On Letter Of Transmittal; Stock Powers and Endorsements.
If this Letter of Transmittal is signed by the registered holder(s) of the
Shares tendered hereby, the signatures(s) must correspond with the name(s) as
written on the face of the certificates without alteration, enlargement or any
change whatsoever.

                                       6
<PAGE>

     If any of the Shares tendered hereby are held of record by two or more
persons, all such persons must sign this Letter of Transmittal.

     If any of the Shares tendered hereby are registered in different names on
different certificates, it will be necessary to complete, sign and submit as
many separate Letters of Transmittal (or facsimiles thereof) as there are
different registrations of certificates.

     If this Letter of Transmittal is signed by the registered holder(s) of the
Shares tendered hereby, no endorsements of certificates or separate stock powers
are required unless payment of the Purchase Price is to be made to, or Shares
not tendered or not purchased are to be registered in the name of, any person
other than the registered holder(s), in which case the certificate(s) evidencing
the Shares tendered hereby must be endorsed or accompanied by appropriate stock
powers, in either case signed exactly as the name(s) of the registered holder(s)
appear(s) on such certificates.  Signatures on any such certificates or stock
powers must be guaranteed by an Eligible Institution. See Instruction 1.

     If this Letter of Transmittal is signed by a person other than the
registered holder(s) of the Shares tendered hereby, certificates evidencing the
Shares tendered hereby must be endorsed or accompanied by appropriate stock
powers, in either case, signed exactly as the name(s) of the registered
holder(s) appear(s) on such certificate(s). Signature(s) on any such
certificates or stock powers must be guaranteed by an Eligible Institution.  See
Instruction 1.

     If this Letter of Transmittal or any certificate or stock power is signed
by a trustee, executor, administrator, guardian, attorney-in-fact, officer of a
corporation or other person acting in a fiduciary or representative capacity,
such person should so indicate when signing, and proper evidence satisfactory to
the Company of the authority of such person so to act must be submitted.

     6.   Stock Transfer Taxes.  The Company will pay or cause to be paid any
stock transfer taxes with respect to the sale and transfer of any Shares to it
or its order pursuant to the Offer.  If, however, payment of the aggregate
Purchase Price is to be made to, or Shares not tendered or not purchased are to
be registered in the name of, any person other than the registered holder(s), or
if tendered Shares are registered in the name of any person other than the
person(s) signing this Letter of Transmittal, the amount of any stock transfer
taxes (whether imposed on the registered holder(s), such other person or
otherwise) payable on account of the transfer to such person will be deducted
from the Purchase Price unless satisfactory evidence of the payment of such
taxes, or exemption therefrom, is submitted. See "The Tender Offer--Acceptance
for Payment and Payment for Shares" in the Offer to Purchase.  Except as
provided in this Instruction 6, it will not be necessary to affix transfer tax
stamps to the certificates representing Shares tendered hereby.

     7.   Special Payment and Delivery Instructions.  If a check for the
Purchase Price of any Shares tendered hereby is to be issued in the name of,
and/or any Shares not tendered or not purchased are to be returned to, a person
other than the person(s) signing this Letter of Transmittal, or if the check
and/or any certificates for Shares not tendered or not purchased are to be
mailed to someone other than the person(s) signing this Letter of Transmittal or
to an address other than that shown above in the box captioned "Description of
Shares Tendered," then the boxes captioned "Special Payment Instructions" and/or
"Special Delivery Instructions" on this Letter of Transmittal should be
completed.

     8.   Substitute Form W-9 and Form W-8.  Under the United States federal
income tax backup withholding rules, unless an exemption applies under the
applicable law and regulations, 31% of the gross

                                       7
<PAGE>

proceeds payable to a stockholder or other payee pursuant to the Offer must be
withheld and remitted to the United States Treasury, unless the stockholder or
other payee provides such person's taxpayer identification number (employer
identification number or social security number) to the Depositary and certifies
that such number is correct. Therefore, each tendering stockholder should
complete and sign the Substitute Form W-9 included as part of the Letter of
Transmittal so as to provide the information and certification necessary to
avoid backup withholding, unless such stockholder otherwise establishes to the
satisfaction of the Depositary that it is not subject to backup withholding.
Certain stockholders (including, among others, all corporations and certain
foreign stockholders (in addition to foreign corporations)) are not subject to
these backup withholding and reporting requirements. In order for a foreign
stockholder to qualify as an exempt recipient, that stockholder must submit an
IRS Form W-8 or a Substitute Form W-8, signed under penalties of perjury,
attesting to that stockholder's exempt status. Such statements may be obtained
from the Depositary.

     9.   Withholding On Foreign Stockholders.  Even if a foreign stockholder
has provided the required certification to avoid backup withholding, the
Depositary will withhold United States federal income taxes equal to 31% of the
gross payments payable to a foreign stockholder or his or her agent unless the
Depositary determines that an exemption from or a reduced rate of withholding is
available pursuant to a tax treaty or that an exemption from withholding is
applicable because such gross proceeds are effectively connected with the
conduct of a trade or business in the United States.  For this purpose, a
foreign stockholder is a stockholder that is not (i) a citizen or resident of
the United States, (ii) a corporation, partnership or other entity created or
organized in or under the laws of the United States, any state or any political
subdivision thereof or (iii) any estate or trust the income of which is subject
to United States federal income taxation regardless of the source of such
income.  In order to obtain a reduced rate of withholding pursuant to a tax
treaty, a foreign stockholder must deliver to the Depositary a properly
completed IRS Form 1001.  In order to obtain an exemption from withholding on
the grounds that the gross proceeds paid pursuant to the Offer are effectively
connected with the conduct of a trade or business within the United States, a
foreign stockholder must deliver to the Depositary a properly completed IRS
Form 4224. The Depositary will determine a stockholder's status as a foreign
stockholder and eligibility for a reduced rate of, or an exemption from,
withholding by reference to outstanding certificates or statements concerning
eligibility for a reduced rate of, or exemption from, withholding (e.g., IRS
Form 1001 or IRS Form 4224) unless facts and circumstances indicate that such
reliance is not warranted. A foreign stockholder may be eligible to obtain a
refund of all or a portion of any tax withheld if such stockholder meets the
"complete redemption," "substantially disproportionate" or "not essentially
equivalent to a dividend" test described in the Offer to Purchase or is
otherwise able to establish that no tax or a reduced amount of tax is due.
Backup withholding generally will not apply to amounts subject to the 30% or
treaty-reduced rate of withholding. Foreign stockholders are urged to consult
their tax advisors regarding the application of United States federal income tax
withholding, including eligibility for a withholding tax reduction or exemption
and refund procedures.

     10.  Requests for Assistance or Additional Copies.  Any question, requests
for assistance or requests for additional copies of the Offer to Purchase, this
Letter of Transmittal or other tender offer materials may be directed to the
Depositary at its telephone number and address listed on the front page of this
document. Requests for such copies will be furnished promptly at the Company's
expense.  Stockholders may also contact their local broker, dealer, commercial
bank or trust company for documents relating to, or assistance concerning, the
Offer.

     11.  Irregularities.  All questions as to the number of Shares to be
accepted and the validity, form, eligibility (including time of receipt) and
acceptance for payment of any tender of Shares will be determined by the
Company, in its sole discretion, which determination shall be final and binding
on all parties.  The

                                       8
<PAGE>

Company reserves the absolute right to reject any or all tenders it determines
not to be in proper form or the acceptance of or payment for which may, in the
opinion of the Company's counsel be unlawful. The Company also reserves the
absolute right to waive any of the conditions of the Offer and any defect or
irregularity in the tender of any particular Shares or any particular
stockholder. No tender of Shares will be deemed to be validly made until all
defects or irregularities have been cured or waived. None of the Company, the
Depositary, or any other person is or will be obligated to give notice of any
defects or irregularities in tenders, and none of them will incur any liability
for failure to give any such notice.

     12.  Lost, Stolen or Destroyed Certificates.  If your certificate(s)
representing Shares have been lost, stolen or destroyed, so indicate on the
front of this Letter of Transmittal.  The Depositary will send you additional
documentation that will need to be completed to effectively surrender such lost,
stolen or destroyed certificates.

     IMPORTANT: THIS LETTER OF TRANSMITTAL (OR A MANUALLY SIGNED FACSIMILE
THEREOF) TOGETHER WITH SHARE CERTIFICATES AND ALL OTHER REQUIRED DOCUMENTS MUST
BE RECEIVED BY THE DEPOSITARY PRIOR TO THE EXPIRATION DATE. STOCKHOLDERS ARE
ENCOURAGED TO RETURN COMPLETED SUBSTITUTE FORM W-9 WITH THEIR LETTER OF
TRANSMITTAL.

                                       9
<PAGE>

            PAYER'S NAME:  Registrar & Transfer Company

________________________________________________________________________________
Substitute Form W-9
Department of the Treasury,
Internal Revenue Service
Payer's Request for Taxpayer Identification Number (TIN)

     CERTIFICATION -- Under penalties of perjury, I certify that (i) the number
shown on page 4 of this form is my correct Taxpayer Identification Number (or I
am waiting for a number to be issued to me) and (ii) I am not subject to backup
withholding because: (a) I am exempt from backup withholding; or (b) I have not
been notified by the IRS that I am subject to backup withholding as a result of
a failure to report all interest or dividends; or (c) the IRS has notified me
that I am no longer subject to backup withholding.

     Certification instructions -- You must cross out Item (ii) above if you
have been notified by the IRS that you are currently subject to backup
withholding because of under reporting interest or dividends on your tax return.

SIGNATURE:____________________________          DATE:___________________________

Name:___________________________________________________________________________
                                 (Please Print)
 Address:  _____________________________________________________________________

           _____________________________________________________________________

           _____________________________________________________________________
                               (Include Zip Code)
________________________________________________________________________________

     NOTE: FAILURE TO COMPLETE AND RETURN THIS FORM MAY RESULT IN BACKUP
WITHHOLDING OF 31% OF ANY PAYMENTS MADE TO YOU PURSUANT TO THIS OFFER. PLEASE
REVIEW THE ENCLOSED GUIDELINES FOR CERTIFICATION OF TAXPAYER IDENTIFICATION
NUMBER ON SUBSTITUTE FORM W-9 FOR ADDITIONAL DETAILS.  YOU MUST COMPLETE THE
FOLLOWING CERTIFICATE IF YOU ARE AWAITING YOUR TIN.

________________________________________________________________________________
             CERTIFICATE OF AWAITING TAXPAYER IDENTIFICATION NUMBER

     I certify under penalties of perjury that a TIN has not been issued to me,
and either (1) I have mailed or delivered an application to receive a TIN to the
appropriate IRS Center or Social Security Administration Office or (2) I intend
to mail or deliver an application in the near future. I understand that if I do
not provide a TIN by the time of payment, 31% of all payments made to me
thereafter will be withheld until I provide a number.

Signature: __________________________           Date:___________________________

________________________________________________________________________________

                                       10