Having a puddle or a wet spot under a vehicle is a sign that the car has a leakage. Finding out whether the fluid is oil involves smelling and noting the color of the fluid.
If a puddle or traces of blackish fluid are found underneath a vehicle, touching and smelling the fluid helps in identifying what it is. Engine oil is usually brown or amber, has a slippery feel when rubbed between the fingers and has a distinctive gassy smell. It also soaks into concrete slowly and leaves a dark residue behind.
If in doubt, remove the dipstick from the engine and compare the fluid on the ground with what is on the dipstick. If they match, it’s possible that the engine oil is leaking. An oil leak can also smell before it is serious enough to leak onto the driveway.