Southwest Airlines is working with some of its corporate clients to launch a sustainable aviation fuel purchasing program, Southwest executives said in a sustainability town hall event this week.

Currently, the carrier is working with four launch customers, whom it will announce later this year, in a beta partnership for shared investment in sustainable aviation fuel, Southwest director of environmental sustainability Helen Giles said. Southwest has acquired a “limited volume” of the fuel, which currently has limited production capabilities and comes at a much higher cost compared with standard jet fuel, for use in 2021 and 2022. The participating companies are able to fund that premium cost over standard jet fuel either with cash or unused UATP funds, and in exchange, they get credit for the related carbon-emissions reduction.

Southwest still is adding some corporate partners to the program, though “space is limited” due to the limited volume of fuel available, she said. The ultimate goal is to support sustainable aviation fuel production, so it eventually is in greater supply and at a cheaper price.

“SAF is critical to decarbonizing aviation,” Giles said. “There’s not a lot of SAF today, and what is out there is really expensive, so it will take the collaboration of everyone to really scale this market.”

Other major U.S. carriers similarly have announced partnerships with corporate customers this year to support sustainable aviation fuel development and use, including Deloitte’s agreements with both Delta Air Lines and American Airlines and United Airlines’ Eco-Skies Alliance.

Southwest later this year also will launch a “green incentive program,” in which corporate partners can earn performance-based funds that they can use for sustainability program initiatives including charitable donations, carbon offsets or sustainable aviation fuel, Giles said. Southwest is in “active conversations” with several customers to launch the program, she said.

Additionally, Southwest has developed a new reporting system for its customers to see their carbon footprints with the carrier, Southwest senior sustainability strategy consultant Jesse Nikkel said. The system uses “actual flight data” that looks at fuel consumed and other parameters on flights used by a company’s travelers to provide carbon reporting, he said.

Systems typically use origin and destination data to estimate carbon footprints, but those do not take into account such factors as the type of aircraft used or whether the flight was nonstop, according to Nikkel.