If they aren't too big, Pour-N-Restore works great. Another alternative which is low cost would be to scrub it with some powder laundry detergent. Use a clean wire brush on the concrete for the rust and it will usually come right up.
Cleaning and removing oil stains are two different functions. As Shea stated Pour N Restore is best for removing oil spots.
The same manufacturer makes a rust stain remover as well. I have never tried it so I do not sell it. I would be happy to try and get a bottle for you as a sample, if you would provide some feedback and get the Oil Stain remover from us