According to the info on this site, anywhere from 19.5 to 28 gallons per barrel. A barrel actually seems to be 42 gallons vs. the 55 gallons I had imagined:
http://www.newton.dep.anl.gov/askasci/eng99/eng99288.htmPlugging those numbers into the calculation it saves 8-11.5 million barrels of oil to come up with the same amount of gasoline. It's not completely true because the other parts of the barrel can be refined into products as well.
Anyway, 8-11.5M bbl x $70/bbl = $560M-$805M
They also forgot to figure in that's the savings PER YEAR. So, on the $3B spent, it will take 3.7 to 5.3 years to equal the reduction in dependence on foreign oil vs. if they had just given out $3B in free gas. Assuming you just gave everyone over the age of 18 a gas gift card, everyone could've got $13.33 worth of gas...