Green’s Dictionary of Slang

1. (also oil) a heavy drinker.

1970		E. Thompson Garden of Sand (1981) 547: When Jack saw the empties already piling up by the door, he knew with Bill it was going to be the same old oil.
1994		N. McCall Makes Me Wanna Holler (1995) 87: The fellas and I called them ‘oilers’ because they drank [...] to loosen their tensions.

2. (US black) one who regularly gets involved in fights.

1944

D. Burley Orig. Hbk of Harlem Jive 19: These young studs are oilers from back.