Do not be alarmed if your aircraft begins to smell suspiciously like a fast-food restaurant – or pond scum for that matter.

US airlines were racing this week to demonstrate their clean energy credentials, scheduling a number of flights powered partially by biofuels.

First United Continental announced the departure on Monday morning of Flight 1403 from Houston for Chicago – or the 'Eco Skies test flight' as the airline called it – using a mix of 60% conventional jet fuel and 40% algae-based fuels.

Alaska Airlines then announced it would operate 75 flights using a mix of 80% conventional jet fuels and 20% biofuels starting on Wednesday. Instead of algae-base, the airline is using used cooking oil or fast-food restaurant throwaways, said Robert Ames, vice-president of Dynamic Fuels, which produced the fuel.

"We can use vegetable oil. We can use used cooking oil," he said. "A good mental reference is McDonald's used fryer grease."

The flights will include 11 between Seattle and Washington DC, and 64 between Seattle and Portland, Oregon, the airline said.

"We wanted to demonstrate the use of sustainable biofuels both on a transcontinental route and on a short haul that competes with ground vehicle traffic," Bobbie Egan, a spokeswoman for Alaska, said in an interview.

The airline calculates the use of the biofuels mix cuts greenhouse gas emissions on those particular flights by 10%.

It's not clear, however, when – or even if – Alaska will begin running regular flights on biofuels.

The cooking oil substitute cost six times as much as conventional jet fuel, said Egan. That makes a permanent switch prohibitively expensive – unless production increases and prices come down.

Dynamic Fuels, a joint-venture between Tyson Foods Inc, the world leader in chicken, beef and pork production, and Syntroleum Corporation, is the only producer of this type of fuel in the US. The plant has been operating just over a year, and has an annual capacity of 75m gallons.

Ames would not discuss current prices, but he said he was hopeful they would eventually come down.

"There is enough used cooking oil," he said. "Are we shutting down Saudi Arabia? The answer clearly is no. In America, we like our fast food but we really don't have those kinds of quantities available."

Monday's flights were not exactly historic. Virgin Atlantic first began trying out biofuels three years ago, and KLM tested a 50/50 blend of conventional fuel and used cooking oil on its Paris-Amsterdam route last June.

The US airforce, meanwhile, plans to test 40 of its aircraft on a biofuels blend by 2013.

But the flights could encourage the rest of the industry move towards cleaner fuels.

Following Monday's flight, Solazyme said on its Facebook page it hoped to sell as much as 20m gallons of biofuel a year beginning in 2014.

"Sustainable biofuels, produced on a large scale at an economically viable price, can one day play a meaningful role in powering everyone's trip on an airline," the chief operating officer of United, Pete McDonald, said in a statement.

Egan said meanwhile she hoped Alaska's move would encourage other biofuels suppliers to get into the market, bringing costs down.

The test flights are also a sharp contrast to threats of a trade war by the US aviation industry to moves by European airports to charge carriers for greenhouse gas emissions.