What oil does every fast food chain fry in?

How chains are classified "Single-source" means one named oil only — Five Guys' peanut, In-N-Out's sunflower, Mission BBQ's soybean. "Vegetable blend" means the chain's label uses "and/or" language across multiple oils (canola, soybean, palm, etc.) — only one is in the fryer on any given day, but the chain doesn't commit to which. "Dedicated fryer" means fries cook in a fryer that never contacts wheat-breaded items or animal proteins — this is the Cold Eight, the eight chains where strict celiacs and vegans can eat fries with confidence. Beef-derived classification covers the Tallow Club: McDonald's natural beef flavor (not actual tallow but beef-flavored), plus the four chains using actual beef tallow in the cooking oil (Steak 'n Shake, Bojangles, Portillo's, Smashburger). Soy classification flags any chain whose cooking oil contains soybean — either as the named oil or as one possibility in an "and/or" blend, since soy is a top-9 allergen.