There is concern over water-in-oil emulsion formation in passenger cars in the field. Crankcase pressure measurements in the ASTM Sequence IID rust test have been used to indicate possible emulsion formation tendencies of lubricants. This paper presents the development of a short duration emulsion fleet test procedure which demonstrates low car-to- car variability and correlates well with a previous fourmonth winter emulsion fleet test. Physical emulsion characteristics and used oil analyses are described. Evaluation of both Sequence IID reference oils and commercial oils in this field test reveals a lack of correlation between Sequence IID crankcase pressure results and field performance.The new procedure has been applied to investigate the impact of additive and base oil variations on the emulsion-forming tendencies of lubricants in the field. Base oil variables such as viscosity grade, composition, and volatility were evaluated. Additive variables included dispersant type and level, viscosity improver type, and detergent metal type. An additive system has been identified which is particularly effective in reducing the formation of water-in-oil emulsions in the field.