United Airlines (UAL) - Get Report , which uses about 4 billion gallons of fuel annually -- making it one of the world's biggest fuel consumers -- also has become the airline industry's leader in seeking to reduce global carbon emissions.

United said it accounts for about 60% of the global aviation industry's commitment to biofuels. It expects to purchase about 900 million gallons of biofuel or 90 million gallons a year for the next 10 years.

According to United figures, Cathay Pacific is second, committed to 413 million gallons of biofuel use, while JetBlue is committed to 109 million gallons, Lufthansa is committed to 42 million gallons and other airlines collectively are committed to about 70 million gallons.

In March, in a demonstration of its commitment, United became the first U.S. airline to use a high percentage of biofuel (about 30%) to power a regularly scheduled flight, which operated between Los Angeles and San Francisco for two weeks.

In a continuing effort, at Los Angeles International Airport, United has spearheaded the inclusion of biofuel (a single-digit percentage) in the airport fuel supply used by all of the airport's carriers.

On Friday, sustainability officers from United, JetBlue and Alaska will discuss their efforts during the final day of a Fort Lauderdale, Fla. conference presented by Jersey City, N.J.-based Companies Vs. Climate Change, which seeks to provide a forum for businesses to discuss climate change solutions.

United is "trying to grow the biofuels industry for aviation," said Natalie Mindrum, the carrier's director of environmental responsibility. "We want to be a leader in this area."

Biofuels are sustainable fuels created from renewable sources, such as agricultural waste and even household wastes, but not, in United's case, from corn or other edible sources. "We are not competing with food sourcing," Mindrum said.

U.S. commercial aviation produces 2% of the nation's man-made greenhouse gas, while driving 5% of GDP, according to figures from Airlines for America.

Most airlines seek to reduce fuel use through the purchase of new aircraft, the installation of winglets on aircraft, and fuel conservation programs such as single-engine taxi, careful calibration of how much fuel to carry and the use of electricity rather than engines when aircraft are on the ground.

But United goes a step farther in its biofuels commitment, which has played out in two efforts.

One is a partnership with AltAir Fuels, a Paramount, Calif.-based biofuel company. United signed its first agreement with Altair in 2009; fuel production begin in March 2016. "We will purchase up to 15 million gallons annually over the next three years," Mindrum said. "This is a small percentage, but we have to start somewhere."

Fuel from AltAir is provided to the fuel farm at LAX, with the result that "every flight {which takes on fuel at LAX} has a small quantity of biofuel," she said.

The bulk of United's potential biofuel use will result from a partnership with Fulcrum BioEnergy, a Pleasanton, Calif.-based company that seeks to convert municipal waste into aviation biofuel.

In 2015, United invested $30 million in Fulcrum, the single largest investment by a U.S. airline in alternate fuel. The two companies envision joint development of up to five projects at United's hubs, expected to produce 180 million gallons of biofuel annually. The first site has yet to be selected.

Fulcrum takes household trash, converts it to gas through one process, and then converts carbon monoxide and hydrogen gases into liquid fuel. Cathay Pacific has also invested in Fulcrum.

Mindrum said the use of Altair fuel reduces carbon dioxide emissions by 60%, while the use of Fulcrum fuel reduces carbon dioxide emissions by 80%. "By using waste, we are not pulling fossil fuels out of the ground," she said. "We are using {materials} that have already been pulled out."

U.S. airlines are all committed to reducing carbon emissions, although the extent of their current commitments vary.

Among the four largest carriers, American (AAL) - Get Report -- which already has the youngest fleet of the network carriers -- takes a new airplane every week. Employees are strongly encouraged to seek out methods to reduce fuel consumption, and the carrier is "evaluating the alternative jet fuel industry and identifying the most promising companies and technologies," said spokesman Matt Miller.

Delta (DAL) - Get Report has reduced fuel burn per available seat mile by 6% since 2008 and is phasing out some older aircraft, such as the Boeing 747 and 50-seat regional jets. It has a program that enables passengers to make financial contributions to offset the environmental impact of its flights.

"We're the only U.S. airline committed to carbon-neutral growth," said spokesman Trebor Banstetter. "We also nabbed the top airline spot for global companies in the 2016 Newsweek Green Rankings, ranking 85th."

Southwest (LUV) - Get Report not only is modernizing its fleet and implementing fuel savings project, but also it signed a 2014 agreement with Red Rock Biofuels to purchase 3 million gallons of biofuel annually.

"This renewable fuel will be refined in Oregon from forest residues, helping to reduce the risk of destructive forest fires," the carrier said on its website. "The blended product of biofuel and jet fuel is expected to be used at Southwest's San Francisco Bay Area operations, with first delivery anticipated in 2018."

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.