Okay, you are dealing with a fairly porous material. It is usually advisable to immediately after installation of just the tile, and after the grout has set up a couple of hours, to seal the surface the first coat with a penetrating sealer.
As it is the approach to extracting the oil is to use Borax soap powder. Sprinkle dry powder over the problem areas to about an 1/8th to 1/4 inch depth. Don't worry if some gets down in the open grout joints. Next cover the area with cardboard and tape the cardboard down. You may need to leave this in place at least a week. In the meantime get the rest of the tiles sealed and even proceed with the grouting. Note of caution: When all go the grouting is not going to be done all at once a person must pay close attention to the grout mixing ratio. (Unless it's a pre-mix of course) Problem being that a different amount of water can produce a different shade of grout color.
After the Borax treatment if any discoloration still exists, you will need a small bottle of "Greased Lightening." Readily available at home improvement stores and sometimes even supermarkets. Vacuum and wipe away all Borax and spray the area quite liberally with the Greased Lightening. Let it sit, but keep it damp, for about 5 minutes. Use a medium bristle brush and scrub in small circles. Wipe it away, let the area dry and get it sealed.
Now, all this being said your other option would be to simply break out the stained tiles, scrape away the adhesive and re place the tiles.
PS... If the adhesive is really hard and difficult to scrape use a propane torch to soften it a little while scraping.