This method is for determining the concentration of acid oils in refinery caustic. Part A separation of the acid oils by gravity, is a rapid determination for control purposes. The acid oil concentration range which can be determined is from 1 liquid volume percent (LV-%) upward, with no maximum limit. Part B separation of the acid oils by extraction, is reserved for a more precise gravimetric procedure as well as a volumetric measurement. It is applicable to caustic samples containing as little as 0.1 wt- % acid oil.