You may be surprised, but kitty litter does an excellent job of absorbing oil. Simply pour fresh kitty litter over the oil stain and let it sit for a few hours. Sweep the kitty litter away and check to see if the stain is gone. If not, you may want to add more kitty litter and keep it on the stain overnight. You can also stir the kitty litter over the stain to help it along as it absorbs the oil.
Dampen the area with water if the driveway is dry, then sprinkle a generous amount of baking soda over the stain. Scrub the baking soda into the stain using a hard scrub brush. You will need to really scrub hard in order for the baking soda to work effectively. You can also use cornstarch or cornmeal if you don't have baking soda around. Rinse off thoroughly.
Apply a concentrated laundry detergent to the oil stain and sprinkle with hot water to make a paste. Scrub the stain vigorously with the hard scrub brush. Let the laundry detergent paste sit on the stain overnight. The next day, add more hot water, and scrub the stain again. Wash the paste off to see how much of the stain you were able to get up. You may need to repeat this once or twice more to fully get the stain out.
Oven cleaner is especially effective at removing oil stains on concrete driveways. First scrub the stain thoroughly with liquid soap and water, then rinse off and dry as much as possible with a towel. Spray the oven cleaner over the stain and scrub it into the stain using a wire scour brush. Allow it to work for an hour or so before rinsing off. Finally, scrub the stain again with soap and water to ensure that all the oven cleaner chemicals are washed away. Use gloves when working oven cleaner as it is toxic and can burn your skin.