The U.S. Environmental Protection Agency and U.S. Department of Agriculture conducted a joint study to determine the effects of using low-lead and unleaded gasoline and non-lead additives in farm equipment. A recreational vehicle engine was also evaluated in the program.The work was completed at the National Institute for Petroleum and Energy Research in Bartlesville, Oklahoma under contract with EPA. This paper reports on the results of this work.The test program evaluated four tractor engines, one combine engine, two farm truck engines and a recreational-vehicle engine. Results showed that medium and higher speed engines experienced valve seat recession using unleaded fuel. Lower speed engines did not show valve seat recession while operating on unleaded fuel. No substantial valve seat recession occurred using 1.2 or 0.10 gm/gal leaded fuel. Tests with alternative additives were found to have potential for reducing valve seat recession. While combustion chamber deposits increase with the use of additives, their long term impact is not known. Other measures of engine wear besides valve seat recession were also looked at and are reported. Besides speed and load it appears that air-fuel ratio and the use of valve rotators may play a role in valve-seat recession.