Avios can be used on a vast number of flights, but not literally "all" flights globally. Avios is the loyalty currency for the International Airlines Group (IAG), so you can primarily use them on British Airways, Iberia, Aer Lingus, and Vueling. Because British Airways is a founding member of the oneworld alliance, you can also use Avios to book "Reward Flights" on partner airlines including American Airlines, Cathay Pacific, Qantas, Qatar Airways, and Japan Airlines. However, availability is the catch: airlines only release a specific number of "reward seats" per flight, so if those are gone, you cannot use Avios for a full redemption. By 2026, the "Avios part-payment" feature has expanded, allowing you to use Avios to reduce the cash price of almost any commercial seat on BA or Iberia, even if a standard reward seat isn't available. You cannot generally use Avios on non-partner budget airlines like Ryanair or EasyJet.