Toyota Prius.....?

That is a very good question. I think the future is with these type of hybrids that can use bio-diesel/electric. If Mercedes with their new diesel engines and Toyota's Hybrid technology were to get together, they could probably create a great system.

But then the big oil companies and Governments probably will not allow this to happen until the price of oil reaches $100. a barrel and people start to demand change.

A diesel is harder to start in an instant like the petrol engine in the Prius does. It would be very difficult to make the transfer from electric to petrol power as seamless as it is at the moment.

By the way, the petrol engine runs a fair bit during city use, although it is a very clean petrol engine compared to some.

I think that, considering the expense as it is, the Prius would have to be incredibly high-priced and reserved only for the elite, which would make Toyota's goal of selling one million hybrid cars a year virtually impossible. However, Priuses get 51 mi/gal on average, that's about 19 more than the average sedan. That's way better, even if it uses regular gas on the highway.

Petrol has far more energy which is easier to tap in order to charge the battery. The diesel would need to be running more in order to ensure the battery didn't run flat, therefore defeating the object of the thing.

All answers so far are WRONG!

Modern diesels are easy to start, far more economical etc...

The answer is that in the US (the target market) diesel cars aren't popular! They don't buy them! Why would Toyota make a car nobody would buy?

err one flawed vehicle! handles like a slab of granite and first thing is petrol motor kicks in to charge and preheat systems so short journeys are all done on petrol anyway! Also the thing is ugly, maybe they should have used the better system from Lexus and stuck it in Corollas and Avensis'.

The gasoline engine starts and stops repeatedly. Diesels don't do that very well. And they're often hard to start at all when it's cold.

probably because a diesel emgine is a lot heavier than a petrol unit,so when its running on just electric it will be even slower

cause it's made in Japan and they don't use commerial diesel fuel.

not at all