http://www.elmhurst.edu/~chm/vchembook/514gasoline.h...
"This fractional distillation process yields approximately 25% of straight-run gasoline from each barrel of crude oil."
"The yield of gasoline may be doubled by converting higher or lower boiling point fractions into hydrocarbons in the gasoline range."

http://www.keystone-web.com/commodities/indepth/ener...
"While the ratio of 3 barrels of crude oil to produce 2 barrels of gasoline and 1 barrel of heating oil is often used, for simplicity assume that 2 barrels of crude produce 1 barrel of gasoline and 1 barrel of heating oil."