Determining the "most sustainable" airline is complex because different carriers lead in different areas, but Air France-KLM and Etihad Airways are frequently cited as global leaders in 2026. Air France-KLM has consistently topped the Dow Jones Sustainability Index due to their aggressive fleet renewal program—replacing older jets with more efficient A350s and A220s—and their massive investment in Sustainable Aviation Fuel (SAF). Meanwhile, Etihad has gained recognition for its "Greenliner" program, which uses a Boeing 787 as a flying laboratory to test carbon-reduction technologies. In the United States, United Airlines is a frontrunner, having committed to being 100% green by 2050 without relying on traditional carbon offsets, instead focusing on direct air capture technology and SAF production. On the low-cost side, Wizz Air often claims to be the most sustainable because they operate one of the youngest fleets in the world with the highest passenger density, resulting in the lowest CO2 emissions per passenger kilometer. Ultimately, sustainability in aviation is currently driven by three factors: the age of the aircraft, the percentage of SAF used, and the elimination of single-use plastics on board, with these carriers setting the industry standard for environmental responsibility.