Burning oil is an example of a free radical, exothermic (heat given off) reaction and entropy is involved as it is for all types of reactions. If entropy is the reason why we get so much heat would mind explaining how endothermic (heat adsorbed) reactions occur. Hint: you need to understand the 1st, 2nd and 3rd laws of thermodynamics. Yes energy is stored in oil, entropy is not the reason.