my oil light came on in my car. i have a bmw 318i. anyone know what kind of oil it needs?

I recommend using 10W-40. It should be o.k. for an older Bimmer. Castrol GTX has always proven to be a good product (IMO).

If it's new-ish, BMW recommends some semi-synthetics.

If you have it, Read your owner's manual!!!

Keep the following in mind:

You should not make a habit of mixing regular and synthetic oils. Since you don't know what kind of oil to put in it, I will have to assume you don't know what kind is in there now.

Whatever type or viscosity of motor oil you put in is better than no oil!

Where is that oil going? It went somewhere. Either its: a) leaking out of the engine, b) leaking into the cooling system, c) leaking past the valve seals, or d) leaking past the piston rings. All are bad but you should hope it's a).

what year is the bimmer? If it is from the mid-90's (E-36 body type), they tend to use thicker oil (10W-40, or even 20W-50)