Lufthansa is to become the first airline to operate commercial flights on 'biofuel', upping the stakes in the race for airlines to prove their green credentials.

The German flag-carrier announced November 29 that it will run commercial flights on a 50-50 mix of biofuel and kerosene from April 2011.

The six month trial period will be conducted using an Airbus A321 flying between Hamburg and Frankfurt and will be used to test the long-term effects of biofuels on engine maintenance and lifespan, Lufthansa said.

Although several major airlines such as Air New Zealand, KLM and Continental have all conducted biofuel tests, Lufthansa believes that it is the first to use the greener fuel on passenger flights.

The fuel used will be Biomass-to-Liquid (BTL) produced fuel and will come from a sustainable supply and production process operated by Neste Oil, a fuel firm from Finland.

It's estimated that Lufthansa will save some 1,500 tonnes of carbon dioxide during the trial, which will be conducted using only one of the aircraft's engines.

Although carriers are at pains to point out that they are a comparatively small contributor to global warming, millions has been invested in biofuel experiments over the past five years.

At the Paris Air Show earlier this year, a consortium led by European aircraft manufacturer Airbus completed the world's first flight using pure biofuel, opening the door to further work to reduce the dependence on kerosene to fuel the growing aviation industry.

British Airways is currently constructing Europe's first sustainable jet fuel plant and plans to use it to produce some 16 million gallons of biofuel annually from 2014, more than enough to make all of its flights from London City Airport carbon neutral.