This paper reviews ASTM's work in developing the new API CH-4 diesel engine oil category for 1998. It focuses in particular on three new engine tests - Cummins M-11, Mack T-9, and Caterpillar 1P - which are juxtaposed on existing engine and bench tests in the API CG-4/CF-4 categories. These new tests ensure increased engine durability, while operating at high temperatures and high levels of soot in the crankcase. The high soot levelsMP expected in 1998 emission-controlled engines are a result of retarded fuel injection timing used to lower NOx, combined with high top-ring piston locations used to minimize particulate.API CH-4 is the most robust API diesel engine oil category ever developed. It improves the quality of diesel engine oils for both existing and new engines, using both low and normal fuel sulfur levels. In addition, it will allow a more flexible approach to oil drain intervals, in accordance with the recommendations of the individual engine manufacturers.