<PAGE>
 
                                                                      Exhibit 11


                           RENTAL SERVICE CORPORATION
                STATEMENT RE: COMPUTATION OF EARNINGS PER SHARE


<TABLE>
<CAPTION>
                                                  Three Months Ended            Nine Months Ended     
                                                     September 30,                 September 30,      
                                                  1996           1995           1996           1995   
                                               -----------   ------------   ------------   -----------
                                                                                                      
<S>                                            <C>            <C>           <C>            <C>        
Weighted average common shares                                                                        
 outstanding                                    6,121,963      4,195,345      5,573,790      4,066,043
                                                                                                      
Net effect of common stock, common                                                                    
 stock options and warrants issued at                                                                 
 less than IPO price within twelve                                                                    
 months, based on the treasury stock                                                                  
 method:                                                                                              
     Common stock                                       -        681,453          6,615        810,761
     Options                                      108,780        152,604        132,336        152,604
     Warrants                                      57,981         60,820         59,895         60,820
                                               ----------     ----------    -----------    -----------
                                                6,288,724      5,090,222      5,772,636      5,090,228
                                               ==========     ==========    ===========    ===========
                                                                                                      
Income (loss) before extraordinary item        $  952,000     $1,021,000    $ 2,179,000    $ 2,939,000
Preferred stock accretion                        (524,000)      (432,000)    (1,643,000)    (1,278,000)
                                               ----------     ----------    -----------    -----------
                                               $  428,000     $  589,000    $   536,000    $ 1,661,000
                                               ==========     ==========    ===========    ===========
                                                                                                      
Net income (loss)                              $ (317,000)    $  543,000    $   910,000    $ 2,461,000
Preferred stock accretion                        (524,000)      (432,000)    (1,643,000)    (1,278,000)
                                               ----------     ----------    -----------    -----------
                                               $ (841,000)    $  111,000    $  (733,000)   $ 1,183,000
                                               ==========     ==========    ===========    ===========
                                                                                                      
Per share amount:                                                                                     
Income (loss) before extraordinary item        $      .07     $      .11    $       .09    $       .32
Extraordinary item                                   (.20)          (.09)          (.22)          (.09)
                                               ----------     ----------    -----------    -----------
Net income (loss)                              $     (.13)    $      .02    $      (.13)   $       .23
                                               ==========     ==========    ===========    ===========
</TABLE>

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