put some kitty litter on it, and rub it into the oil (like with an old shoe preferably), then leave it on there for at least a day, then sweep it up.
Go to a hardware store and get some concrete degreaser.
I have no idea of how to remove it but I can tell you how to prevent it. Next time paint the concrete where your car is gonna be. If its outside the garage I would pick a grey color like the driveway so it doesnt look tacky.
pressure washing/home depot will assist with excellent products, etc.