You guys think you are doing it tough!
A litre of petrol where I live is $A1.50, this equates to $US5.10/US gallon.
I drive a 3.6L V6 Holden (Oz GM car) that has a factory fitted fuel injected LPG (Liquid Petroleum Gas) system fitted. LPG here sells for $2.18/US gallon, I get about 8km/ltr average fuel consumption, that equates to 18.9miles/US gallon, or about 11.5c/mile.
Car is dual fuel, so it can still run on petrol, automatically starts on petrol, then sequentially (ie cylinder by cylinder) changes from petrol to LPG.
The reason for the low cost of LPG is that the Govt does not put an excise on LPG like they do for petrol, they want to encourage the use of LPG as we have so much of it and we import petrol. They even pay a subsidy of $A2000 to people that have their car converted to run on LPG.