And unfortunately it's chemically expressed trans-fat oil.
We'd all be better off if they went back to the traditional use of tallow.
You're about 13 years behind. McD's (or almost any US franchise) doesn't use trans fat oils anymore.
I think McD's uses liquid oil, so not hydrogenated (trans fat). You hydrogenate oil to make it solid at room temperature, as a substitute for animal fats. If you're going to fry in it there's no point in not starting with an oil that is liquid at room temperature.