汽油 (gas, as in state of matter + oil) refers to petrol/gasoline, the kind you put in cars.

石油 (stone oil) is refers to oil, as in the natural resource (such as crude).

原油 (origin oil) refers specifically to crude oil.

柴油 (kindling oil) refers to diesel.

加油 (add oil) is used to mean refilling the car with petrol.

And finally, 机油 (motor oil) is engine oil.