Emissions systems durability is influenced by many engine oil formulation variables. Previous studies have suggested that emissions system durability is optimized by a high metal/phosphorus ratio. Tn this work a systematic study was conducted to determine the effect of phosphorus and phosphorus-free additives in the lubricant on exhaust emissions using an engine dynamometer for 22 minutes. Within experimental accuracy, both phosphorus-free lubricant have shown satisfactory engine performance characteristics and similar HC emissions under identical engine test conditions. However, there might be a marginal improvement of carbon monoxide emission by phosphorus-free oils over the phosphorus-containing oils.