How much electricity and natural gas is used to explore for petroleum, extract it, transport it, refine to gasoline (or diesel, etc.), transport it again, and then pump it into your tank?
Some sites I've found that are trying to answer this question:
Gasoline and Oil
Electricity vs Oil - Planet Better Place
Just to refine the oil to make gasoline, it may take 3kWh or 7.5kWh (plus many therms of natural gas?), so for the refining alone, it could be used to move an EV 30-50 miles -- without using the gasoline!
Can you confirm/deny/correct these numbers?