Diesel powered cars already rival regular hybrid-electric gasoline cars in the economy stakes, and it’s only a matter of time until manufacturers combine the two fuel-saving technologies to build the ultimate fuel-miser. The limiting factor currently is the high costs involved but that may change if governments subsidize development costs by taxing cars based on carbon dioxide emissions.

According to Autoweek, there are several manufacturers working on a reliable diesel-hybrid platform. France’s PSA Group has long insisted that gasoline hybrids never made sense because the CO2 levels are the same as diesels and the costs are high. The company has already produced two prototypes using a Peugeot 307 and Citroen C4 body. Each emits less than 90g/km of CO2. By comparison, Toyota’s Prius emits 104g/km.

Currently, consumers would have to pay an extra $5,000 for a diesel powered hybrid, but the PSA Group is working on bringing that figure below $3,300. There has also been news that the European government may enforce mandatory limits for carbon emissions set at 120g/km in the near future. A diesel powered hybrid is probably the best option manufacturers have right now on reaching that standard.