I'm not sure about this but I know it could be looked up. McD's used an oil that contained some beef tallow for flavor. Don't remember what the other ingredients were.

Then when the big blow up about using beef tallow happened, McD had to remove beef tallow from the ingredients of their fries. They have a huge research budget so found some kind of oil mixture and flavoring to get the original taste back without the beef tallow.

So the McD fries are still pretty good. Not my favorite though.