The aim of the present work is to prepare waste fried oil methyl ester (WFOME) as a diesel fuel substitute. High viscosity and poor volatility are the major limitations of waste fried oil for utilization as a fuel in diesel engines. The cost of waste fried oil methyl ester (WFOME) production is presented in this paper and found to be more economical than mineral diesel. WFOME satisfies the important fuel properties as per ASTM specification of biodiesel. This paper discusses the results of investigations carried out on a single-cylinder, four-stroke, direct-injection, diesel engine operated on methyl esters of waste fried oil blended with mineral diesel. The performance of the engine with diesel was considered as the baseline data. The performance parameters for different WFOME blends were found to be very close to diesel and the emission characteristics of engine improved significantly. At rated output, brake thermal efficiency of blend B50 (50% biodiesel + 50% mineral diesel) found 6.5% lower than that of diesel. For B50, brake specific consumption observed was 6.89% higher than that of diesel. CO emissions were reduced by 21-45% for different blends. The particulate matters were lower by 23-47%. Because of insignificant sulfur content, the sulfur dioxide emissions were lower by 50-100% for different blends. (C) 2010 Elsevier Ltd. All rights reserved.