Yesterday a commercial Alaska Airlines plane pumped with a blend of traditional jet fuel and wood biofuel flew from Seattle to Reagan National Airport in Washington, D.C.

The flight was the first to use a 20 percent blend of biofuel made of leftover wood from timber harvests in the Pacific Northwest. It’s not the first to use a biofuel mixture in general though—in June, Alaska Airlines flew two test flights on jet fuel mixed with biofuel made from non-edible parts of corn, and in March of this year, United Airlines pledged to use a 30 percent biofuel mixture on its flights from Los Angeles to San Francisco. The United Airlines fuel is produced by a company called AltAir Fuels that depends on a variety of biological source materials “from used cooking oil to algae.”

Alaska Airlines’ wood-based fuel was developed by a Colorado-based company called Gevo, which partnered with the Northwest Advanced Renewables Alliance (NARA) to develop the wood waste into isobutanol, which it then converted to jet fuel. Gevo also created the corn waste biofuel mixture that Alaska Airlines flew with in June.

Gevo said that the wood used in its process was limbs, stumps, and branches leftover from timber harvests in managed forests and on private land. This “forest residual” is sometimes burned, so using it to create biofuel can prevent related air pollution.

In an e-mail to Ars, a Gevo representative said that the Alcohol-To-Jet (ATJ) fuel the company supplied to Alaska Airlines “provides about 2 percent more energy because of its tailored composition. This means more miles flown per gallon of fuel.” It’s also free of pollutants commonly contained in jet fuel like sulfur, the representative said.

Aviation is low on the list of ways to sustainably travel, and the industry notably got a pass on reining in its emissions in the Paris Agreement. But in October the International Civil Aviation Organization agreed to a voluntary carbon offsetting scheme—which isn’t the same as reducing emissions but has been seen as a place to start. Although airlines have been open to using biofuels as a percentage of jet fuel, the main hurdle to the plan is cost. In 2001 Alaska Airlines flew 75 flights on a 20 percent biofuel mix but it discontinued the experiment after those flight runs.

Update: In a comment to Ars, Alaska Airlines admitted the wood fuel project was pricey and experimental in nature: “Monday’s demonstration flight was part of a nearly $40 million project to produce fuel for one flight only. While we are very interested in finding a long-term, sustainable aviation biofuel, we don’t have any current plans for additional flights using the forest residual biofuel. Right now there is not an adequate supply to do more than the one."

But the demonstration opened the possibility that biofuel could become more common in planes. In a statement on Thursday, Alaska Airlines Senior Vice President of Communications Joe Sprague said that were Alaska Airlines to replace all of its fuel with a 20 percent biofuel mixture, it would “be the equivalent of taking 30,000 cars off the highways in the Seattle region.”