SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                 SCHEDULE 13D/A
                    Under the Securities Exchange Act of 1934
                               (Amendment No. 20)

                              Quanta Services, Inc.
                              ---------------------
                                (Name of Issuer)

                        Common Stock, $0.00001 par value
                        --------------------------------
                         (Title of Class of Securities)

                                    74762E102
                                    ---------
                                 (CUSIP Number)

       Leslie J. Parrette, Jr., Senior Vice President, General Counsel and
       -------------------------------------------------------------------
                              Corporate Secretary
                              -------------------
                              UtiliCorp United Inc.
                              ---------------------
        20 West Ninth Street, Kansas City, Missouri 64105 (816) 421-6600
        ----------------------------------------------------------------
                  (Name, Address and Telephone Number of Person
                Authorized to Receive Notices and Communications)

                                February 8, 2002
             (Date of Event which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report
the acquisition that is the subject of this Schedule 13D, and is filing this
schedule because of Rule 13d-1(e), 13d-1(f), or 13d-1(g), check the following
box. / /

NOTE: Schedules filed in paper format shall include a signed original and five
copies of the schedule, including all exhibits. See Section 240.13d-7(b) for
other parties to whom copies are to be sent.

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).



                               CUSIP No. 74762E102
--------------------------------------------------------------------------------
     1    NAMES OF REPORTING PERSONS
          I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (entities only)

          UtiliCorp United Inc. #440541877
--------------------------------------------------------------------------------
     2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (See Instructions)
          (a)
          (b)  X
--------------------------------------------------------------------------------
     3    SEC USE ONLY

--------------------------------------------------------------------------------
     4    SOURCE OF FUNDS (See Instructions)

          WC, BK
--------------------------------------------------------------------------------
     5    CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO
          ITEMS 2(d) or 2(e)

--------------------------------------------------------------------------------
     6    CITIZENSHIP OR PLACE OR ORGANIZATION

          Delaware
--------------------------------------------------------------------------------
  NUMBER OF SHARES            7    SOLE VOTING POWER
 BENEFICIALLY OWNED
 BY EACH REPORTING                 29,243,179
    PERSON WITH
                              --------------------------------------------------
                              8    SHARED VOTING POWER
                                   None*
                              --------------------------------------------------
                              9    SOLE DISPOSITIVE POWER
                                   29,243,179
                              --------------------------------------------------
                              10   SHARED DISPOSITIVE POWER
                                   None
--------------------------------------------------------------------------------
     11   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
          29,243,179
--------------------------------------------------------------------------------
     12   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES
          (See Instructions)
          X
--------------------------------------------------------------------------------
     13   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
          38.06%**
--------------------------------------------------------------------------------
     14   TYPE OF REPORTING PERSON (See Instructions)
          CO
--------------------------------------------------------------------------------

*    This representation is qualified by the fact that, as described in Item 4
     of the Schedule 13D, UtiliCorp has the ability to vote or direct the vote
     of the shares subject to the Stockholder's Voting Agreements only in two
     limited, tax-related circumstances. UtiliCorp expressly disclaims
     beneficial ownership to any shares of Common Stock that are subject to the
     Stockholder's Voting Agreements.

**   The percentage reflected in row 13 above is obtained by using 76,829,934
     shares as the denominator (in accordance with Rule 13d-3(d)(1)(i)(B)). This
     denominator includes: (a) 59,605,129 shares of Issuer's issued and
     outstanding Common Stock (as indicated in Issuer's Form 10-Q filed on
     November 14, 2001), and (b) 17,224,805 shares of Common Stock into which
     Issuer's Convertible Preferred Stock held by UtiliCorp is convertible.


                                       2


     Also note that the percentage of Common Stock owned by UtiliCorp on a
     partially diluted basis is approximately 36.04%. This percentage is
     obtained by using 81,145,385 shares as the denominator, which includes (a)
     the 76,829,934 shares discussed in the previous paragraph, (b) 1,152,055
     shares of Limited Vote Common Stock (as indicated in Issuer's Form 10-Q
     filed on November 14, 2001), and (c) 3,163,396 shares of Common Stock into
     which the Issuer's Convertible Subordinated Notes can be converted.
     UtiliCorp's ownership can be further diluted by (x) other classes of
     Issuer's securities that can be converted into Common Stock and (y) shares
     of Common Stock issuable under Issuer's Stock Option Plan.


                                       3


                               AMENDMENT NO. 20 TO
                            STATEMENT ON SCHEDULE 13D

INTRODUCTION

     All information herein with respect to UtiliCorp United Inc., a Delaware
corporation ("UTILICORP"), and the common stock, par value $0.00001 per share
(the "COMMON STOCK"), of Quanta Services, Inc., a Delaware corporation ("ISSUER"
or "QUANTA"), is correct to the best knowledge and belief of UtiliCorp. The
Schedule 13D originally filed on October 4, 1999 on behalf of UtiliCorp and
nineteen amendments thereto filed on October 8, 1999, October 14, 1999, October
20, 1999, October 26, 1999, November 9, 1999, January 13, 2000, April 27, 2000,
May 25, 2000, June 20, 2000, July 17, 2000, May 23, 2001, October 1, 2001,
October 4, 2001, October 11, 2001, October 19, 2001, October 30, 2001, November
13, 2001, and November 28, 2001, respectively, on behalf of UtiliCorp are
incorporated by reference and amended as follows.

ITEM 4. PURPOSE OF TRANSACTION.

     As previously disclosed in amendments to this Schedule 13D, UtiliCorp has
been engaged for several months in discussions with Quanta concerning
UtiliCorp's desire to elect a majority of the directors to Quanta's board in
order to achieve financial statement consolidation for financial reporting
purposes with respect to Quanta. These discussions were recently abandoned for a
second time. During the course of these protracted negotiations, Quanta's board
of directors authorized actions that UtiliCorp believes violated an agreement
between UtiliCorp and Quanta concerning UtiliCorp's right to purchase Quanta's
stock. These actions, together with Quanta's disappointing financial
performance, have caused UtiliCorp to re-evaluate its prior support of Quanta's
current board of directors.

     Accordingly, UtiliCorp has advised Quanta that it intends to present an
opposition slate of nominees for election as directors at Quanta's 2002 annual
meeting of stockholders. UtiliCorp's slate will be named within the time period
required by Quanta's bylaws and will consist of six individuals that are
affiliated with UtiliCorp and three that are independent from both UtiliCorp and
Quanta. The UtiliCorp-nominated slate of directors is expected to exhibit and
promote business objectives, goals, and values that are reflective of those of
UtiliCorp.

     If elected, UtiliCorp's nominees are expected to implement a long-term
business plan aimed at maximizing the value of Quanta. In addition, UtiliCorp
may pursue short-term initiatives designed to bring significant value to
Quanta's stockholders. For instance, UtiliCorp is contemplating, subject to
price and other considerations, the implementation of a stock repurchase program
in the range of 20% to 25% of Quanta's outstanding shares. The repurchase
program could take the form of a third-party or an issuer self-tender offer.
Alternatively, upon obtaining control of the Quanta board, UtiliCorp may
initiate a sale process for Quanta (in which UtiliCorp may or may not be a
participant) or may consider appropriate unsolicited offers to acquire Quanta.

     UtiliCorp intends to canvass other stockholders of Quanta in order to
assess their views concerning the strategic direction of Quanta. The input of
these stockholders will be considered by UtiliCorp in formulating its definitive
plans and proposals to maximize the value of Quanta. To assist UtiliCorp in
formalizing the strategy that will guide the UtiliCorp director nominees to
Quanta's board, UtiliCorp is currently in the process of retaining an investment
banking firm to act as a financial advisor.

     Notwithstanding UtiliCorp's misgivings about the actions recently taken by
Quanta's board and the overall performance of Quanta's management team as
reflected in Quanta's recent financial performance, UtiliCorp continues to
believe that certain of Quanta's existing management and employees


                                       4


are important to its future. Accordingly, if UtiliCorp's nominees are elected at
Quanta's 2002 annual meeting of stockholders, they are expected to support a
broad-based retention program directed at Quanta's key employees, including
certain executive management employees.


                                       5


                                    SIGNATURE

     After reasonable inquiry and to the best of the undersigned's knowledge and
belief, the undersigned hereby certifies that the information set forth in this
statement is true, complete and correct.

Dated: February 8, 2002                 UtiliCorp United Inc.

                                        By:       /s/ Leslie J. Parrette, Jr.
                                        Name:     Leslie J. Parrette, Jr.
                                        Title:    Senior Vice President,
                                                  General Counsel and Corporate
                                                  Secretary


                                       6