1. If you spawn on or travel to a snowy biome (if you are ballsy enough) this is an assumption, but there should be rocks that have oil
2. *basilosaurus noises* for some reason i never see anyone get basilos in their ARK playthroughs but they are just americas way to get infinite oil (they produce it passively when tamed) to tame one, just go to the basilosaurus tips tab, its that easy.
3. Oil chunks, usuaally found around E V E R Y W H E R E in the sea and they look like little black chunks with a DNA trail of oil slowly bubbling up, so grab an Itchy, a good damage pick, and start diggin
(Island, Mobile) I tend to get my oil from oily rocks up in the north, snowy, area on the very west side where there are icy islands in the water. The oily rocks are all over the icy islands! Hope this was helpful :)
if you can’t find a critter that drops oil, i found quite a lot of oil rocks in the northern region (mobile, island map), around the shore. be weary of wolves and argies. rexes too, but typically they’re preoccupied with mammoths or rhinos. hope this helped!