United Airlines Flies Historic Passenger Flight With 100% Sustainable Fuel

United Airlines this week became the first commercial carrier to fly a full passenger flight using 100% sustainable aviation fuel.

The historic flight, which took off on Wednesday, flew more than 100 passengers from Chicago's O'Hare International Airport to Washington, D.C.'s Reagan National Airport on a 737 MAX 8. The flight used 500 gallons of sustainable fuel (or SAF) in one engine and the same amount of conventional jet fuel in the other engine as airlines can only use up to 50% of SAF on board, according to the airline.

"United continues to lead from the front when it comes to climate change action," the airline's CEO Scott Kirby, who was on board for the eco-friendly flight, said in a statement. "Today's SAF flight is not only a significant milestone for efforts to decarbonize our industry, but when combined with the surge in commitments to produce and purchase alternative fuels, we're demonstrating the scalable and impactful way companies can join together and play a role in addressing the biggest challenge of our lifetimes."

Overall this year, United purchased more than 7 million gallons of SAF, which it said produces nearly 80% greenhouse gas emissions reductions over its lifecycle, compared to conventional jet fuel.

United has pledged to reduce its greenhouse gas emissions by 100% by 2050 without relying on traditional carbon offsets (a somewhat controversial practice).

Airlines have been moving to become more environmentally friendly and reduce their carbon footprint in recent years. Earlier this year, British Airways flew a completely carbon neutral flight from London to Glasgow using a combination of sustainable aviation fuel, carbon offsets, and other emissions-reducing measures like switching to half-power during taxiing. And other carriers have committed to offset their carbon emissions in recent years, including Delta, JetBlue, and Qantas.

Alison Fox is a contributing writer for Travel + Leisure. When she's not in New York City, she likes to spend her time at the beach or exploring new destinations and hopes to visit every country in the world. Follow her adventures on Instagram.