I am interested, how would you say "motor oil" (the one that you put in your car engine) in Latin? Would it be "oleum" or "unguentum" or maybe something else?
Rock oils, now called by the modern Greek-Latin word, petroleum, were in ancient times called bitumen by the Romans:
Babylone lacus amplissima magnitudine, qui limne asphaltitis appellatur, habet supra natans liquidum bitumen; quo bitumine et latere testaceo structum murum Sameramis circumdedit Babylonem. ("At Babylon there is a lake of wide extent which is called the Asphalt Lake, with liquid bitumen floating on it. Semiramis built a wall round Babylon of this bitumen and burnt-brick.") --Vitruvius
oleum itself is the oil of pressed olives. unguen refers properly to grease, but is also used when speaking of lubricating oils (Cato On Agriculture 146.2). The verb for oiling something is ungo. If you do not like the term petroleum, you could coin a term like motoroleum or motorileum or maybe use unguen the same way.