I haven't yet gone through all their supporting math to evaluate their comparison but this is interesting. The eGallon: How Much Cheaper Is It to Drive on Electricity? | Department of Energy

From the DOE's methodology PDF (pardon the lack of formatting): eGallon Methodology The eGallon is measured as an “implicit” cost of a gallon of gasoline. It is calculated by multiplying the average U.S. residential electricity price (EP) by the average comparable passenger car adjusted combined fuel economy (FE) by the average fuel consumption of popular electric vehicles (EC), as follows: eGallon ($/gal) = FE * EC * EP where FE = the average comparable passenger car adjusted combined fuel economy, miles/gallon EC = the average electricity consumption (kWh/mi) of the top 5 selling PEVs in the U.S., and EP = the average U.S. electricity price, $/kWh. For instance, if the average comparable 2012 passenger car adjusted combined fuel economy, mi/gal is 28.2 mi/gal and the average efficiency for the top selling U.S. EV brands in 2012 is .35kwh/mi, the price of an e-gallon would be: 28.2 mi/gal * .35 kWh/mi * .1233 $/kWh = $1.22/gal In other words, it costs about $1.22 to drive an EV the same distance that a vehicle powered by an internal combustion engine (ICE) can go on a gallon of gasoline. I'll have to chew on this for awhile.

Where does "average" come from? Is this a rolling metric, or is a snapshot taken once a year at a specific time so you have a rating like "eGallon2012"? Is it U.S. market vehicles? Just from a skim of the text this reads to me like statistic * statistic * statistic * statistic = garbage.

I think the author of the web page was going for nothing more ambitious than showing newbies that it's cheaper to drive an EV than an ICE. You can roll your own value for cost per eGallon by substituting different values for comparable ICE mi/gal, EV kWh/mi, and your electricity cost per kWh.

I don't see the point of this. Calculate cents per mile (km) for each and let the actually-real-world-comparable numbers stand for themselves.

I think it's more informative to consider miles per dollar. If my Model S can go 100 miles for $3.30 (30 kWh x $0.11 per kWh), that's $0.03 per mile, or 30 miles per dollar. If the ICE car goes 100 miles for $11.81 ((100 / 28.2 mpg) x $3.33), that's $0.12 per mile, or 8.5 miles per dollar. More like 4x in this case.