This work aims at studying the combined effect of oxygen enrichment and emulsification techniques on engine performance behavior of a compression ignition engine fuelled with WCO (waste cooking oil) as fuel. Used sunflower oil collected from a restaurant was chosen as fuel. A single cylinder, water cooled, agricultural oriented, diesel engine was used for the experiments. Initially tests were performed using neat diesel and neat WCO as fuels. Performance, emission, and combustion parameters were obtained. In the second phase of work, WCO was converted into its emulsion by emulsification process using water and ethanol and tested. In the third phase, the engine intake system was modified to admit excess oxygen along with air to test the engine with WCO and WCO emulsion as fuels under oxygen enriched environment. A comparative study was made at 100% and 40% of the maximum load (i.e. 3.7 kW power output) at the rated engine speed of 1500 rpm. Neat WCO resulted in reduced BTE (brake thermal efficiency), increased smoke, HC (hydrocarbon) and CO (carbon monoxide) emissions. The maximum BTE was noted as 26.2% with neat WCO, whereas it was 30.5% with diesel at the maximum power output of 3.7 kW. The smoke, emission was noted to be 75% with neat WCO and 40% with diesel. WCO emulsion resulted in improved BTE as compared to neat WCO. It was achieved as 28.2% with WCO emulsion. The smoke and NOx values were noted to be less than neat WCO. Oxygen enrichment further improved the engine’s performance with significant reduction in emissions such as smoke, HC and CO with neat WCO and WCO emulsion as fuels. 24% of oxygen concentration was found to be optimal for best operation for both WCO and WCO emulsion. At peak power output the maximum brake thermal efficiencies were noted to be 28.4% and 29.6% with neat WCO and WCO emulsion respectively for the oxygen concentration of 24%. However, NOx increased to 685 ppm and 590 ppm with WCO and its emulsion respectively for 24% of O2 at 100% load. From the experimental results, it was concluded that WCO could be effectively used as fuel in a single cylinder diesel engine by making stable emulsion with water and ethanol. The WCO emulsion could be used directly in the unmodified engine with superior performance and significant reduction in all emissions mainly at high power outputs. Oxygen enrichment could offer considerable improvement in BTE, significant reduction in smoke, HC and CO emissions at both power outputs with neat WCO as fuel. Oxygen enrichment could further improve the performance and reduced emissions of the WCO emulsion even at part load (i.e. 40% load). 24% oxygen concentration by volume could be recommended for optimal operation with WCO and its emulsions as fuel. Combined operation of oxygen enrichment and emulsification could achieve significant improvement in the engine performance at all operating conditions with NOx under control using WCO as fuel.