Abstract: The apparatus provides for a housing mountable on a trailer for conducting the process in-situ. A pump withdraws substantially all hydrocarbon-contaminated matter from the oil waste pit and delivers it into a lower chamber formed in the housing, wherein the hydrocarbon-contaminated matter is separated from the heavy solid particles and heavy salt water. The hydrocarbon-containing mixture, after being separated in the lower housing is delivered into the upper chamber formed in the housing and heated to facilitate separation, by gravity, of hydrocarbons, water and fine particles into various layers for subsequent withdrawal from the housing. The process of withdrawal of the hydrocarbon-contaminated mixture continues until hydrocarbon content of the oil waste pit is reduced to such degree that the waste pit becomes substantially hydrocarbon-free and is environmentally safe.