The chief of the Opec oil cartel has warned that investing in biofuels could push oil prices "through the roof", the Financial Times has reported.
Opec secretary general Abdalla El-Badri said moves to use biofuels would make his members consider cutting investment in new oil production, the FT said.
President Bush says the US will cut petrol use by 20% in 10 years, partly through increased use of biofuels.
Opec members control about 40% of the world's oil production.
Mr El-Badri said that while Opec members had so far maintained their investment plans, he added: "If we are unable to see a security of demand... we may revisit investment in the long term."
The warning comes as leaders of the G8 industrialised nations gather for their summit in Germany.
Environmental issues are high on the agenda and the use of biofuels is central to the attempts of many G8 countries to cut their carbon emissions.
Biofuels can be anything made with vegetable matter that burns. They can be used to replace some or all of the petrol used in vehicles.
Our Take: This should make the U.S. all the more determined to become energy independent. These energy thugs think they have us by the proverbial balls because we're currently the largest importer and consumer of crude and refined petrofuels. Let them do what they want. We should strive for a day where OPEC proclamations and actions are essentially irrelevant to fuel prices and the American economy. Let's fast-track Ethanol and Biodiesel R&D, as well as research and developments on vehicles such as the Chevy Volt, which promise a combined 100+ miles per gallon in conjunction with plug-in technology.