Bio-fuel production provides an alternative non-fossil fuel without the need to redesign current engine technology. This study presents an experimental investigation into the effects of using biodiesel blends on diesel engine performance and its emissions. The biodiesel fuels were produced from Sunflower oil using the transesterification process with low molecular weight alcohols and sodium. hydroxide then tested on a steady state engine test rig using a Euro 4 four cylinder CI (compression ignition) engine. This study also shows how by blending biodiesel with diesel fuel at intervals of B5, B10, B15, and 820 can decrease harmful gas emissions significantly while maintaining similar performance output and efficiency. Production optimization was achieved by changing the variables which included methanol/oil molar ratio, NaOH catalyst concentration, reaction time, reaction temperature, and rate of mixing to maximize biodiesel yield. The technique used was the RSM (response surface methodology). In addition, a second-order model was developed to predict the biodiesel yield if the production criteria is known. The model was validated using additional experimental testing. It was determined that the catalyst concentration and molar ratio of methanol to sunflower oil were the most influential variables affecting percentage conversion to fuel and percentage initial absorbance. (C) 2013 Elsevier Ltd. All rights reserved.