I bought a bottle of lukus octane booster...that stuff really works...you put a bottle into your gas tank in my case 25 to 30 gallons...if your tank is smaller I guess you would use half a botle..anyway..my mountain mpg went from 16.5 to 19 mpg...stp also has a cheaper booster..I will probably get 24 or 25 mpg on the hwy..