Optimum Octane Number for Unleaded Gasoline

Current evidence indicates that cars manufactured after 1974 or 1975 will be required to operate on unleaded gasoline. To determine the level of octane quality justified when refineries are producing only unleaded gasoline, improvements in mileage attainable by using gasoline of higher octane number were compared to costs of raising octane number. Motorists' total gasoline costs per mile are lowest when the octane number of the unleaded gasoline pool is in the range of 85 to 87 Motor octane number. And, dividing the unleaded pool into at least two octane grades -- one at 1 or 2 units above and one at 2 or 3 units below the pool value -- maximizes car satisfaction for any given pool quality.