Expert: Dave Russell - 6/16/2008

Question
what is the difference between unleaded gasoline and leaded gasoline?

Answer
Leaded gas was manufactured by using tetraethyl lead as an additive. The purpose of the additive was to increase the octane of the gas. Octane is an 8 carbon hydrocarbon molecule which is the standard for measurement of horsepower in internal combusion engines. In the refining process you get a spectrum of various cuts some have lower octane which will cause the engine to knock and run rough. The tetraethyl lead allows the refineries to use a lower grade of gasoline and it's cheaper to produce because it is less refined. The effect is to take fuel that has a 60 or 70 octane rating and raise the rating to the low 80's to mid 90's which the standard and premium brands have.

Hope that helps.