Starting in October 1993, the sulfur in diesel fuel will be lowered from 0.27 wt % average to 0.05 wt % maximum in order to reduce particulate sulfate emissions from on-highway vehicles. Given such a major change in diesel fuel, the study reported here focused on determining the most appropriate crankcase oils to choose.Using low-sulfur fuel, the study assessed the effects of crankcase oils on: emissions, wear, deposits, oil consumption, viscosity, and Total Base Number (TBN) depletion rates. The engines used were 1994 engines with low oil consumption and direct injection, such as the Detroit Diesel Company (DDC) Series 60, Caterpillar 3176B, Mack E-7, and the Caterpillar single-cylinder engine, which will be used in establishing the next oil category to be announced in 1995. The oils evaluated were SAE 10W-30 and 15W-40 oils with sulfated-ash levels of 1.0, 0.5, and 0.0 wt %.The study found that, with low-sulfur fuel, oils need not change significantly from the current quality levels of SAE 15W-40 and API CF-4/SH oils that have a sulfated-ash level of 1.0 wt %. It was also found that oil-base depletion rates will be lower than current rates. This creates an opportunity to lengthen the intervals between oil drains-provided the oil gives adequate control over piston deposits, wear, and viscosity.Low-sulfur fuel has no detrimental effects on engines. There is even some evidence to suggest that it may enhance engine durability at normal oil-drain intervals.