Crankcase emissions from four different Diesel engines, using four different types of lubricating oils, were analyzed for volatile nitrosamines. The results showed large differences in nitrosamine output between different crankcase oils tested in the same engine. Composite emission rates of NDMA from the heavy duty diesel engines tested ranged from 4.4 to 136 μg/hr. Large differences were also observed when the same brand of oil was used in different engines. The controlling factors appear to be the nitrosamine producing capacity of the oils, the NOx levels in the crankcase, and the emission flow rate from the crankcase.