The Sequence IID engine test procedure, traditionally used to evaluate the anti-rust performance of lubricants, has also been used to measure emulsion forming tendencies of lubricants. In the IID engine, emulsion collects at the base of the crankcase ventilation breather tube condenser which causes partial plugging and an increase in crankcase pressure. The purpose of this paper is to describe the chemical nature of the emulsion and to elucidate physical factors which have been found to influence emulsion buildup on the lower face of the Sequence IID condenser. The process of emulsion formation was observed in real time using a fiber optic video camera which aided in understanding the influences of condenser face roughness and lubricant chemistry on crankcase pressure. The effect of substituting unleaded fuel for standard Sequence l!D leaded fuel was also determined. Finally, an abbreviated version of the Sequence IID procedure was used in conjunction with proprietary bench-scale tests to suggest formulation solutions that prevent excessive crankcase pressure buildup in the Sequence IID engine.