The aim of the present work is to experimentally investigate the effect of compression ratio on performance of compression ignition engine operated with waste fried oil methyl ester (WFOME) blended with mineral diesel. This paper discusses the results of investigations carried out on a single-cylinder, four-stroke, direct injection, diesel engine operated on WFOME blended with mineral diesel. Compression ratios considered for this analysis were 14.5, 16.5 and 17.5. All tests with different fuels were conducted for constant speed (1500 rpm) and with varying loads (0.5 kW to 4 kW) on the engine. Comparative measures of brake thermal efficiency, brake specific fuel consumption, exhaust gas temperature, particulate matter, NO and CO have been presented and discussed. Engine performance in terms of higher brake thermal efficiency and lower emissions with different blends of biodiesel (B0, B50 and B70) was observed. The performance parameters for different WFOME blends were found to be very close to diesel and the emission characteristics of engine improved significantly. It was observed from this experimentation that an increase of load leads to a significant increase of break thermal efficiency and decrease in BSFC. The effect of variation in the compression ratio on brake thermal efficiency indicated that higher compression ratios improve the engine efficiency. The best results for BSFC were obtained at increased CR. The results showed that CO and particulate matter emissions decreased while nitrogen oxide emission increased with an increase in CR. For all tested fuels an increase in compression ratio leads to an increase in exhaust gas temperature. The reductions in exhaust emissions and brake specific fuel consumption together with increased brake power, and brake thermal efficiency made the WFOME from waste fried oil a suitable alternative fuel for diesel at higher compression ratios and thus could help in controlling air pollution. (C) 2014 Elsevier B.V. All rights reserved.