One of the most frustrating moments in home ownership must be finding oil stains on your shop floor. However it happened, and regardless of who is to blame, the problem is almost irreversible while there are a number of do-it-yourself home remedies, they only serve to help mitigate the stain, rather than erasing it completely. If you have an oil stain, it will likely remain there forever, even if it may only be a subtle shadow.
Wouldn't it be better to take easy steps to prevent any oil stains in the first place? Your garage floor is likely made of concrete, one of the most durable materials on earth. 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 the oil 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.
Silane/Siloxane blend sealers like Siloxa-Tek 8505 (water based) or Siloxa-Tek 8510 (solvent based) would be a good option for a concrete shop floor. The silane/siloxane has larger particles that offer a more comprehensive surface protection and these particular products are formulated with a proprietary fluropolymer to make them resistant to staining.
However, an epoxy like the Epoxy 325 and a urethane topcoat like the Urethane 645 would be the best option if you are looking for an incredibly durable coating. The built up 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. They also make cleaning extremely easy and leave a beautiful gloss finish, available clear or colored.