United Airlines flew more than 100 passengers to Washington, D.C. this week on a plane with one engine running on 100 percent sustainable aviation fuel.
The Boeing 737 MAX 8 used 500 gallons of sustainable aviation fuel in one engine and the same amount of conventional jet fuel in the other engine to further prove there are no operational differences between the two.
Also, Federal Aviation Administration regulations limit the use of sustainable aviation fuel to 50 percent of all fuel on board.
Sustainable aviation fuel is made with non-petroleum feedstocks, such as biomass from plants, animal waste fat, solid waste from homes such as paper and food scraps and even used cooking oil, according to oil industry company BP.
United recently agreed to purchase 1.5 billion gallons of sustainable aviation fuel from Alder Fuels - enough to fly more than 57 million passengers and is also an investor in Fulcrum BioEnergy.