It would be the first time in the company's illustrious 92-year history that any of its cars had been powered by diesel.
It had previously said that wealthy Bentley owners were "not interested" in economic diesel engines, but Ferdinand Piech, the chairman of the VW group which owns the brand, said: "You will see diesels at Bentley."
At the recent Qatar Motor Show, one of the most important showcases for top-of-the-range manufacturers in the Middle East, Mr Piech confirmed to a trade magazine that the company was working on a secret project to give at least some of its range diesel power.
Bentley cars consume a notoriously large amount of petrol. The miles-per-gallon figure for the current models – from the £126,000 Continental to the Mulsanne at £229,000 – average just 17.
But Bentley is aware that the addition of a diesel engine option could boost sales in Europe as well as improve economy and reduce emissions.
The firm's sales and marketing chief Alasdair Stewart has confirmed that Bentley is investigating diesel power, even though in its two fastest-growing markets in China and America buyers still favour petrol-driven cars.
Diesel engines can be far more powerful, as well as more fuel efficient. Diesel cars have won the last few Le Mans 24 hour endurance races.
Mercedes, BMW and Jaguar all now sell a significant number of diesel-powered cars in spite of the fact the fuel is more expensive in the UK and many new petrol-drive cars are now offering similar economy.