Your garage floor is likely made of concrete, which has the distinction of being incredibly durable. However, it is also a material made up of crushed stone, cement, water, and air, all of which have bound to form concrete. The negative to this mixture is the large number of tiny air bubbles that naturally occur in concrete; these air bubbles are what let oil and other vehicle leakages seep into the material, as well being what makes it so difficult to fully remove stains.
In order to effectively protect your garage floor from stains, oil or otherwise, you need to seal your floor with a good concrete sealer. Concrete sealers help protect your concrete from natural elements, such as water damage, as well as from inadvertent error, like the spilling of oil. However, as there are a number of different chemical formulas for concrete sealers, you want to find the product that best suits your needs: protection from oil stains.
Siloxa-Tek 8505 is a water based penetrating sealer formulated using molecular nano technology and is an excellent solution for a concrete garage floor. For oil stains, the key is to seal off the surface of the concrete, which this silane-siloxane blended sealer will do. Since the 8505 is formulated with a fluropolymer it is able to resist staining from oils and greases forming an olephobic barrier at the surface preventing the passage of fluids. The surface protection will leave the oil pooled on top of the concrete for an easy clean up, rather than leaking into the pores of the concrete to leave a nasty stain. If you are sealing a larger garage floor, or are looking for a higher performing version, the Siloxa-Tek 8510 is the solvent based counterpart to the Siloxa-Tek 8505.
The other choice is the Epoxy 325 primer coupled with the Urethane 645 topcoat. These two sealers work in conjunction to provide comprehensive protection for your garage floor from abrasions, chemicals, oil stains, and more. The Epoxy 325 bonds directly to the concrete substrate, and the Urethane 645 is a clear topcoat that will bind to the Epoxy 325, further increasing the protection.