Originally Posted by
A_Pommie
If a diesel hybrid would be so great why did toyota not use a diesel in the pious?
Simply because there is no market. The biggest market for the Prius is in the USA where the diesel fuel is not ubiquitous and more expensive (per liter) than gasoline.
It would also be difficult to obtain the PZEV certification with a diesel engine as the NOx and particulate emissions are greater.
In addition, diesel fuel takes more oil than gasoline to be produced, thus the net efficiency versus the crude oil is reduced.