UPDATE... I divided incorrectly in the last step. As pointed out by Rik and evnow, the analysis below is not correct. This analysis actually indicates 22,587,642,000 kWh / 132,488,160,000 gallons of gasoline = 0.17 kWh per gallon of gasoline in the refining process.
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Based on my personal analysis the shows that in 2005 US oil refineries consumed 5.86 kWh of electricity for every gallon of gasoline they produced. That same electricity could instead propel a Nissan Leaf over 20 miles.
Analysis and links
Electricity consumption by petroleum refineries in the US in 2005 was 48,891,000,000 kWh
http://www.nationmaster.com/graph/ene_ele_con_by_pet_ref-energy-electricity-consumption-petroleum-refineries#source
Gasoline composed 46.2% of all US refined oil products in 2005
http://tonto.eia.doe.gov/dnav/pet/pet_pnp_pct_dc_nus_pct_a.htm
Therefore, we take 46.2% of the total electricity used by the US refineries in 2005 for galoline production. So that would be 22,587,642,000 kWh of electricity. (48,891,000,000 kWh * .462)
In 2005 US refineries produced 132.4 billion gallons of gasoline
http://www.eia.gov/dnav/pet/hist/LeafHandler.ashx?n=pet&s=wgfrpus2&f=w
Download the spreadsheet and use the 2005 data on gasoline production. The data is the weekly U.S. Refinery and Blender Adjusted Net Production of Finished Motor Gasoline (Thousand Barrels per Day). So you need to add up the weekly totals, multiply by 7 to get the full weeks, multiply by 1000 (data is thousands), and multiply by 42 because there are 42 gallons in a barrel. That gets you to 132,488,160,000 gallons.
132,488,160,000 gallons of gasoline / 22,587,642,000 kWh = 5.86 kWh of electricity consumed for every gallon of gasoline produced in the US in 2005.
I would still like to know how Nissan came up with their 7.5 kWh of electricity consumed for every gallon of gasoline produced. I doubt refineries have become less efficient over the last five years. But I feel like this quick, back of the napkin analysis, could defend the assertion that at least 5 kWh of electricity is consumed for every gallon of gasoline produced. And the data shows that gasoline production consumes far more electricity than most people realize.