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                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
 
                                  SCHEDULE 13G
 
                   UNDER THE SECURITIES EXCHANGE ACT OF 1934
                              (AMENDMENT NO.    )*
 
                                   Sonic Corp.
- --------------------------------------------------------------------------------
                                (Name of Issuer)
 
                                  Common Stock
- --------------------------------------------------------------------------------
                         (Title of Class of Securities)
 
                                    835451105
- --------------------------------------------------------------------------------
                                 (CUSIP Number)
 
Check the following box if a fee is being paid with this /X/ statement. (A fee
is not required only if the filing person: (1) has a previous statement on file
reporting beneficial ownership of more than five percent of the class of
securities described in Item 1; and (2) has filed no amendment subsequent
thereto reporting beneficial ownership of five percent or less of such class.)
(See Rule 13d-7.)
 
*The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter the
disclosures provided in a prior cover page.
 
The information required in 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).
 
                        (Continued on following page(s))
 
                               Page 1 of 4 Pages
 
SEC 1745 (10-85)
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CUSIP NO. 835451105                   13G                     PAGE 2 OF 4 PAGES
 
   
- --------------------------------------------------------------------------------------------------------------
  1   NAME OF REPORTING PERSON
      S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
      Massachusetts Financial Services Company ("MFS")
         I.R.S. Identification No.:   04-2747644
- --------------------------------------------------------------------------------------------------------------
  2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
 
      (a)  / /       (b)  / /
- --------------------------------------------------------------------------------------------------------------
  3   SEC USE ONLY
- --------------------------------------------------------------------------------------------------------------
  4   CITIZENSHIP OR PLACE OF ORGANIZATION
 
      Delaware
- --------------------------------------------------------------------------------------------------------------
      NUMBER OF      5     SOLE VOTING POWER
       SHARES              1,311,200 shares of common stock
    BENEFICIALLY     ------------------------------------------------------------------------------------------
      OWNED BY       6     SHARED VOTING POWER
        EACH         ------------------------------------------------------------------------------------------      
      REPORTING      7     SOLE DISPOSITIVE POWER
       PERSON              1,380,750 shares of common stock
        WITH         ------------------------------------------------------------------------------------------      
                     8     SHARED DISPOSITIVE POWER
- ---------------------------------------------------------------------------------------------------------------
  9   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
         1,380,750 shares of common stock which is also beneficially owned by certain other non-reporting
         entities as well as MFS.
- --------------------------------------------------------------------------------------------------------------
 10   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*
- --------------------------------------------------------------------------------------------------------------
 11   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
         11.9%
- --------------------------------------------------------------------------------------------------------------
 12   TYPE OF REPORTING PERSON*
      IA
- --------------------------------------------------------------------------------------------------------------
 


 
                      *SEE INSTRUCTION BEFORE FILLING OUT!
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SCHEDULE 13G                                                   Page 3 of 4 Pages
 
             
Item 1:     (a)    Name of Issuer:
                   Sonic Corp.
            (b)    Address of Issuer's Principal Executive Offices:
                   101 Park Avenue 
                   Oklahoma City, OK 73102
Item 2:     (a)    Name of Person Filing:
                   Massachusetts Financial Services Company ("MFS")
            (b)    Address of Principal Business Office or, if none, Residence:
                   500 Boylston Street
                   Boston, MA 02116
            (c)    Citizenship:
                   See Item 4 on page 2
            (d)    Title of Class of Securities:
                   Common Stock
            (e)    CUSIP Number:
                   835451105
Item 3:            See Item 12 on page 2
Item 4:     (a)    Amount Beneficially Owned:
                   See Item 9 on page 2
            (b)    Percent of Class:
                   See Item 11 on page 2
            (c)    Number of shares as to which such person has:
                   See Items 5 and 7 on page 2


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SCHEDULE 13G                                                   Page 4 of 4 Pages
 
                
Item 5:            Ownership of Five Percent or Less of a Class:
                   INAPPLICABLE
Item 6:            Ownership of More than Five Percent on Behalf of Another Person:
                   INAPPLICABLE
Item 7:            Identification and Classification of the Subsidiary Which Acquired
                   the Security Being Reported on By the Parent Holding Company:
                   INAPPLICABLE
Item 8:            Identification and Classification of Members of the Group:
                   INAPPLICABLE
Item 9:            Notice of Dissolution of Group:
                   INAPPLICABLE
Item 10:           Certification:


 
         By signing below I certify that to the best of my knowledge and belief,
the securities referred to above were acquired in the ordinary course of
business and were not acquired for the purpose of and do not have the effect of
changing or influencing the control of the issuer of such securities and were
not acquired in connection with or as a participant in any transaction having
such purposes or effect.
         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.
 
Date: November 15, 1995
 
Massachusetts Financial Services Company
 
      
By:       ARNOLD D. SCOTT
   --------------------------------
          Arnold D. Scott
 Senior Executive Vice President,
      Secretary and Director