A complaint by an environmentalist objecting to the line in an advert which said biofuels are "sustainable" has been upheld.
The Advertising Standards Authority (ASA) has said biofuels should not be referred to in this way as the term was misleading.
After the advert appeared in the national press, environmentalist George Monbiot objected to the line: "Biofuels - a sustainable answer to Opec's oil."
In the form of an open letter, the advert was addressed to the president of Opec (Organisation of the Petroleum Exporting Countries).
The body of the text read: "We are proud of our efforts to provide a lower priced, renewable fuel to the world today. This movement toward diversified energy supplies, increased efficiency and greater competition is crucial to the sustainability of future generations, including those in Opec nations."
The letter was signed by the Renewable Fuels Association (RFA), the Canadian Renewable Fuels Association, the European Bioethanol Fuel Association and the Sugarcane Industry Association.
The RFA said they believed the fuels met with a dictionary definition of sustainability because they were "able to be sustained" while "avoiding depletion of natural resources".
Once seen as the solution to cutting greenhouse gas emissions from road transport, many are now concerned biofuels could damage the environment and add to increasing food costs.
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