The airline industry is betting big on sustainable aviation fuel, or SAF—a fuel alternative made from renewable biomass and waste products. Dozens of airlines around the globe are experimenting with it; in November, headlines buzzed following the first fully SAF-powered transatlantic flight on a commercial airline (British carrier Virgin Atlantic). But while the emissions-heavy airline sector is heralding SAF as a silver bullet to its decarbonization goals, experts say environmental pitfalls and other obstacles abound.