Porsche's head of research, Wolfgang Dürheimer, has said that Porsche is not ruling diesel out completely.

Earlier this year he told Automobilwoche that Porsche would not consider offering a diesel engine as a means of complying with future CO2 emissions limits.

Back then, Dürheimer said that diesel is not an alternative for the company because in the segments in which Porsche competes CO2 emissions would still be well above the required level.

He was quoted by Automobilwoche as saying: "In general diesel cars emit much less CO2 than their gasoline counterparts - however the diesel engine emits more NOx and particulates so, on balance, its environmental impact is no better than that of a gasoline engine. This fact is often overlooked."

In his latest interview with Automobilwoche, Dürheimer did say that Porsche was not currently developing a diesel engine because it does not make sense to have the technology just for one market - namely for Europe. It would also be most suitable for just one Porsche model - namely the Cayenne.

However he would not rule diesel out completely and said that Porsche is keeping a close on the technology.

Dürheimer also commented on the pressure on vehicle manufacturers to produce more small cars as a means of reducing average CO2 emissions.

"If we produced a small car like the Smart we would become a different manufacturer - we would be compelled to be a higher volume manufacturer," he said.