The flight makes United the second carrier worldwide to use a biofuel blended with traditional jet fuel, which was first done in September by KLM, a Dutch airline, CNNMoney reported Monday.
United said it was "the first U.S. airline to fly passengers using a blend of sustainable, advanced biofuel and traditional petroleum-derived jet fuel."
"The idea is to validate the technical feasibility and hopefully create enough demand where the alternative energy sources become economically valid," said Robert Mann, an airline industry consultant.
Some considered the flight a green-friendly publicity stunt, CNNMoney said.
To substantially increase the amount of biofuel used by airlines, the biofuel has to come down in price, analysts say.
Still, "any of the percentage of the fuel you can transfer from this Wild West aviation fuel market to a contractual, stable agricultural-based fuel source makes this a real win," said George Hoffer, an economist at the University of Richmond in Virginia.