Thanks for the info guys. Always helps to know what options there are and any warnings on what not to use (ouch).
Since this depends on the size of a spill, at the moment I'm looking at a worst case scenario. But how realistic is the chance of spilling a large quantity of oil? Even if I purchase a large container of oil, I would store it in the garage and fill smaller, sturdier and better containers to take inside. And the size would depend on what I'm using it for.
I'm not concerned about 'stains' on the concrete considering the floor will get covered when the time comes for the machines to go. That won't happen in my lifetime but I don't want to leave any serious issues to someone else in the family. My logic is any oil that reaches the concrete will mean two things, a nightmare to clean and a permanent odor. The membrane idea is good but if oil is getting past the flooring that means cleaning both above and below the flooring... and if the oil can reach the membrane, how far will it spread?
Adhesive tiles sould like a better approach but I don't know enough about them. Even if the oil can't get past the adhesive can it be absorbed into the tile... i.e. around the edges? Maybe some would and others wouldn't depending on what the tile is made of. Something I would need to check. If such a tile exists that won't absorb the oil, when the time comes it could always be covered with carpeting.
If all the above fails, then there are only a couple things I can think of.
A one piece floor covering for at least that area of the room.
Some sort of tray large enough and sturdy enough to placed under each machine. I have no clue if anything like this exists but it's not beyond me to make something if I need to.