A study was made of passenger car engine oil drain intervals from 1946 to the present time. The drain intervals were intercompared with engine tests used to gauge oil performance and trends in automotive emission control.Preliminary data from vehicle tests show that the technology may be available to achieve longer drain intervals in today's automobiles. With the stipulation that the extended drain capabilities of an oil formulation must be qualified in relation to the type of service and the type of gasoline used (i.e., leaded or unleaded fuel), taxicab data show that higher quality levels then current API SE are needed to double today's recommended oil change intervals. Engine wear appears to be the major technical limitation on extending oil change intervals. Other technical limitations are control of engine deposits and resistance to oil thickening.