The energy problems and global warming has led to intense research into the existence of alternative fuels with high efficiency and high calorific value. Oily plants have a high calorific value when using the resulting oil, especially palm oil. The search for alternative fuels has always conflicted with the use of edible oils.

This paper aims to study the effect of cooking times on biodiesel production from oil. The study was applied to different samples of used waste cooking oil (WCO) for several times, the samples were fresh oil, oil cooked for several times: 3, 6, 9 and more than 9 times (local WCO).

The best yield of biodiesel is about 97% for local WCO. The biodiesel color is clear as the Lovibond No. dwindles down which means less FFA% and good quality of biodiesel. This method can be using to decrease density and viscosity of biodiesel and oil to be like diesel. The best preheated temperatures are 60 °C for biodiesel and about 100°C for oil. Cetane number increased with increasing number of using oil . The local WCO is the best Cetane number. But Calorific value is best with fresh oil and local WCO. The local WCO is the optimum selection condition .