Ouch! Poor cat.
The main thing is to prevent the cat ingesting the stuff, so any solution is likely to be a little drastic.
First thing, ask a vet, soonest.
On the other hand, a cat we had got soaked in cooking oil - not nearly as unpleasant as motor-oil - and we used loads of french chalk and talcum powder, brushed through the fur to remove the worst, and then subjected the poor little bastard to a blood-heat bath wrapped in a towel and with lashings of baby shampoo.
The cat hated every second of it, and hared off into a far corner of the house for several hours afterwards, but it did seem to shift the oil. Not so much that it didn't stop the cat having the shits for a day or so afterwards so - again - do whatever you can to stop the cat licking the oil off.
Good luck, and get some thick leather gauntlets!