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                                                                     EXHIBIT 4.6

                                                                        [LOGO]
                                   AROC INC.
                      4200 East Shelly Drive, Suite 1000
                             Tulsa, Oklahoma 74135

                                 June 29, 2001

Dear Stockholders:

     We are offering to purchase any and all of the outstanding shares of our
common stock (the "Shares") from existing stockholders for a purchase price of
$0.06 per share, net to the seller in cash (the "Offer"). THIS OFFER IS NOT
CONDITIONED UPON ANY MINIMUM NUMBER OF SHARES BEING TENDERED.  This Offer was
originally commented on May 14, 2001, and has now been extended until 5:00 p.m.
New York City time, on July 19, 2001, unless further extended or earlier
terminated.  IF YOU HAVE ALREADY TENDERED YOUR SHARES OF AROC COMMON STOCK
PURSUANT TO OUR EARLIER MAILING OF TENDER OFFER DOCUMENTS, NO FURTHER ACTION IS
REQUIRED ON YOUR PART UNLESS YOU WISH TO WITHDRAW YOUR SHARES. IF YOU DO WISH TO
WITHDRAW YOUR SHARES, PLEASE SEE "THE TENDER OFFER--WITHDRAWAL RIGHTS" ON PAGE
25 OF THE OFFER TO PURCHASE.

     Although the offer is being made to all holders of the shares, MPAC
Energy, LLC, our largest stockholder, has advised us that it does not intend to
tender any Shares pursuant to this Offer. MPAC has also advised us that, after
the Offer is consummated, it will pursue a transaction in which AROC will be
taken private and the remaining public stockholders will receive cash for their
shares. As a result, MPAC will own 100% of AROC and we will no longer be a
public company.

     Even if a second-step transaction does not occur, it is nevertheless likely
that the Shares will no longer be quoted on the Pink Sheets Electronic Quotation
Service and AROC will no longer file reports with the SEC.  Under these
circumstances, we would become a private company with all remaining
stockholders, other than MPAC, holding a minority equity position.

     THE PUBLIC MARKET FOR THE SHARES IS VIRTUALLY NONEXISTENT.  WE BELIEVE THAT
THIS MARKET WILL CONTINUE TO BE CHARACTERIZED BY LOW PRICES AND LOW TRADING
VOLUMES FOR THE FORESEEABLE FUTURE.  THIS OFFER PROVIDES THE STOCKHOLDERS WITH
AN OPPORTUNITY TO SELL THEIR SHARES AT A PRICE HIGHER THAN THOSE RECENTLY
AVAILABLE IN THE PUBLIC MARKET.

     The Offer is explained in detailed in the enclosed Offer to Purchase and
Letter of Transmittal.  We encourage you to read these materials carefully
before making any decision with respect to the Offer.  The instructions on how
to tender Shares are also explained in detail in the accompanying materials.

     Prior to the date of this letter, the sales price per share for AROC's
common stock, as reported on June 18, 2001 on the Pink Sheets Electronic
Quotation Service was $0.042.  Any stockholder tendering shares directly to the
Depositary will receive the net purchase price of $0.06 per share in cash and
will not generally incur the usual transaction costs associated with open-market
sales.

     A special committee of the board of directors of AROC (the "Special
Committee"), consisting of the independent director of the board, has determined
that a price of $0.06 per share is fair from a financial point of view to
unaffiliated stockholders.  The Special Committee received a fairness opinion
from its financial advisor, Randall & Dewey, Inc., that a price of $0.06 per
share was fair to the unaffiliated stockholders from a financial point of view.
The Special Committee recommends that the unaffiliated stockholders accept the
Offer and tender their shares pursuant to the Offer.

     The Offer will expire at 5:00 p.m., New York City time, on July 19, 2001,
unless further extended or earlier terminated by AROC.  If you have any
questions or requests for assistance or for additional copies of the Offer to
Purchase, the Letter of Transmittal and the Notice of Guaranteed Delivery, you
may call Registrar and Transfer Company at (800) 368-5948.

                                    Sincerely,

                                    Frank A. Lodzinski
                                    President and Chief Executive Officer<PAGE>

                                                                     EXHIBIT 4.7

            GUIDELINES FOR CERTIFICATION OF TAXPAYER IDENTIFICATION
                         NUMBER ON SUBSTITUTE FORM W-9

OBTAINING A NUMBER

     If you do not have a taxpayer identification number or you don't know your
number, obtain Form SS-5, Application for a Social Security Card, or Form SS-4,
Application for Employer Identification Number, at the local office of the
Social Security Administration or the Internal Revenue Service (the "IRS") and
apply for a number.  You may also obtain Form SS-4 by calling the IRS at
1-800-TAX-FORM.

PAYEES EXEMPT FROM BACKUP WITHHOLDING

     Payees specifically exempted from backup withholding on ALL payments
include the following:

     .   An organization exempt from tax under section 501(a), or an individual
         retirement account.
     .   The United States or any wholly-owned agency or instrumentality
         thereof.
     .   A State, the District of Columbia, a possession of the United States or
         any political subdivision or wholly-owned agency or instrumentality
         thereof.
     .   A foreign government, a political subdivision of a foreign government,
         or any wholly-owned agency or instrumentality thereof.
     .   An international organization or any wholly-owned agency, or
         instrumentality thereof.

     Payees specifically exempted from backup withholding on interest and
dividend payments include the following:

     .   A corporation.
     .   A financial institution.
     .   A dealer in securities or commodities required to register in the U.S.,
         the District of Columbia, or a possession of the U.S.
     .   A real estate investment trust.
     .   A common trust fund operated by a bank under section 584(a).
     .   An exempt charitable remainder trust, or a non-exempt trust described
         in section 4947.
     .   An entity registered at all times during the tax year under the
         Investment Company Act of 1940.
     .   A foreign central bank of issue.
     .   A middleman known in the investment community as a nominee or who is
         listed in the most recent publication of the American Society of
         Corporate Secretaries, Inc. Nominee List.

     Payments of dividends and patronage dividends not generally subject to
backup withholding include the following:

     .   Payments to nonresident aliens subject to withholding under
         section 1441.
     .   Payments to partnerships not engaged in a trade or business in the U.S.
         and which have at least one nonresident partner.
<PAGE>

     .   Payments of patronage dividends not paid in money.
     .   Payments made by certain foreign organizations.
     .   Section 404(k) payments made by an ESOP.

     Payments of interest not generally subject to backup withholding include
the following:

     .   Payments of interest on obligations issued by individuals. Note: You
         may be subject to backup withholding if this interest is $600 or more
         and is paid in the course of the payer's trade or business and you have
         not provided your correct identification number to the payer.
     .   Payments of Tax-exempt interest (including exempt-interest dividends
         under section 852).
     .   Payments described in Section 6049(b) (5) to non-resident aliens.
     .   Payments on tax-free covenant bonds under section 1451.
     .   Payments made by certain foreign organizations.

     Exempt payees described above should file the Substitute Form W-9 to avoid
possible erroneous backup withholding.  FILE THE SUBSTITUTE FORM W-9 WITH THE
PAYER.  FURNISH YOUR TAXPAYER IDENTIFICATION NUMBER, CHECK THE BOX MARKED
"EXEMPT" IN PART II OF THE SUBSTITUTE FORM W-9 AND RETURN IT TO THE PAYER.

     Certain payments other than dividends that are not subject to information
reporting are also not subject to backup withholding.  For details, see sections
6041, 6041A, 6045, 605A, 6050N and the regulations thereunder.

     PRIVACY ACT NOTICE--Section 6109 requires most recipients of dividend,
interest, or other payments to give taxpayer identification numbers to payers
who must report the payments to IRS.  The IRS uses the numbers for
identification purposes and to help verify the accuracy of tax returns.  The IRS
also may provide this information to the Department of Justice for civil and
criminal litigation and to cities, states, and the District of Columbia to carry
out their tax laws.  Payers must be given the numbers whether or not recipients
are required to file tax returns.  Payers must generally withhold 31% of taxable
interest, dividends, and certain other payments to a payee who does not furnish
a taxpayer identification number to a payer.  Certain penalties may also apply.

PENALTIES

     (1)  Penalty for Failure to Furnish Taxpayer Identification Number.  If you
fail to furnish your taxpayer identification number to a payer, you are subject
to a penalty of $50 for each such failure unless your failure is due to
reasonable cause and not to willful neglect.

     (2)  Civil Penalty for False Information with Respect to Withholding.  If
you make a false statement with no reasonable basis which results in no
imposition of backup withholding, you are subject to a penalty of $500.

     (3)  Criminal Penalty For Falsifying Information.  Willfully falsifying
certifications or affirmations may subject you to criminal penalties including
fines and/or imprisonment.

                                       2<PAGE>

                                                                     EXHIBIT 4.8

          INSTRUCTIONS WITH RESPECT TO THE OFFER TO PURCHASE FOR CASH
                  ANY AND ALL OUTSTANDING SHARES OF AROC INC.

     The undersigned acknowledge(s) receipt of your letter and the enclosed
Offer to Purchase, dated June 29, 2001, and the related Letter of Transmittal
(which, together with the Offer to Purchase and any amendments or supplements
hereto or thereto, collectively, constitute the "Offer") in connection with the
offer by AROC Inc., a Delaware corporation (the "Company"), to purchase any and
all outstanding shares of common stock, $0.001 par value per share (the
"Shares"), of the Company at a price of $0.06 per Share, net to the seller in
cash, upon the terms and subject to the conditions set forth in the Offer.

     IF YOU HAVE ALREADY TENDERED YOUR SHARES OF AROC COMMON STOCK PURSUANT TO
OUR EARLIER MAILING OF TENDER OFFER DOCUMENTS, NO FURTHER ACTION IS REQUIRED ON
YOUR PART UNLESS YOU WISH TO WITHDRAW YOUR SHARES.  IF YOU DO WISH TO WITHDRAW
YOUR SHARES, PLEASE SEE "THE TENDER OFFER--WITHDRAWAL RIGHTS."

     This will instruct you to tender the number of Shares indicated below (or
if no number is indicated below, all Shares) that are held by you for the
account of the undersigned, upon the terms and subject to the conditions set
forth in the Offer.

Date :
      ----------------------

Number of Shares to the Tendered*:
                                  -----
Name(s):                                    SIGN HERE:

                                            Signatures(s):
---------------------------------------                  -----------------------
(PLEASE TYPE OR PRINT)                                       (SIGNATURE)

                                            Signatures(s):
---------------------------------------                  -----------------------
(PLEASE TYPE OR PRINT)                                       (SIGNATURE)

Address:

---------------------------------------
---------------------------------------
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           (include zip code)

AREA CODE AND TELEPHONE NUMBER:     (    )
                                    -----------------------------------------

TAXPAYER I.D. OR SOCIAL SECURITY:
                                    -----------------------------------------

------------------------
*  Unless otherwise indicated, it will be assumed that all Shares held by us for
   your account are to be tendered.

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