Holthusen said his company's participation in marketing biofuels extracted from food was driven by economics or legislation.

"If we have the choice today, then we will not use this route," Malaysia-based Holthusen said at a seminar in Singapore.

"We think morally it is inappropriate because what we are doing here is using food and turning it into fuel. If you look at Africa, there are still countries that have a lack of food, people are starving, and because we are more wealthy we use food and turn it into fuel. This is not what we would like to see. But sometimes economics force you to do it."

The world's top commercially produced biofuels are ethanol and biodiesel.

Ethanol, mostly used in the United States and Brazil, is produced from sugar cane and beets and can also be derived from grains such as corn and wheat. Biodiesel, used in Europe, is extracted from the continent's predominant oil crop, rapeseed, and can also be produced from palm and coconut.

Holthusen said Shell has been working on biofuels that can be extracted from plant waste and wood chips, but he did not say when the alternative biofuel might be commercially available.

"We are not resting. We are doing what everybody needs to do. We have worked over time on an alternative to get away from food, and this is what we call the second generation of biofuels," he said.