Abstract: Previous studies have shown that there is a lack of correlation between engine oil phosphorus volatility with both oil volatility and the initial level of phosphorus in the engine oil. On the other hand, these and more recent studies have illustrated that phosphorus volatility is related to temperature, other additives in the oil, and the chemical composition of the zinc di-organo di-thio phosphate (ZDDP) used. This paper reports the results of continued studies associated with engine oil phosphorus volatility, with the ultimate goal of reducing the amount of phosphorus that deposits on catalytic converters adversely affecting catalyst function.