First thing that came up with my google search  shows an accepted value of 8kwh  to produce one US gallon .
my EV Landy is not what you would call an efficient EV  but for the purposes of the argument  it used an average of 33kwh per 100km  over the last 12 months / 4600km  , 
 
 on petrol it used to drink a tad over  20l/100km   or 5.28 US gallons /100km   5.28 x 8kwh equiv to   42.25 kwh/100km 
Thats just efficiency,  As well if we are talking emissions  , Petrol / diesel pollutes twice   1st  from  mining & the refining oil   & 2nd from burning the oil  when  driving the car , so EV  clearly better for the environment .  
How gas cars use more electricity to go 100 miles than EVs do | Autoblog
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