Oil economy is the one quality of a new engine oil that can be most readily observed by the customer. Studies have been made of the relative oil economies of a series of test oils using three different testing environments. These were laboratory engines, a tire test fleet, and an 80 car employee fleet test. All three methods generally ranked oils in the same order, but the size of the differences varied somewhat from method to method.These tests were then used to demonstrate the effects viscosity index improvers and detergent-dispersant packages have on the consumption characteristics of engine oils. They showed that increasing the concentration of viscosity index improvers did not return a proportionate improvement in oil economy. Simple reblending of older multigrade oils to meet the new SAE requirement for measuring the oil’s viscosity at 0 F may result in an oil with significantly poorer economy. It was also found that a 10W-40 oil can give better oil economy than single-grade SAE 30 or 40 oils.The longer crankcase oil drain interval recommendations in the new car owner’s manuals have increased the chances for the car owner to detect a difference in economy between two oils.