The upcoming 2010 plug-in Prius will be able to travel just over 12 miles on electric power only.  Though 12 miles is well short of the 40 plus miles of the upcoming Chevy Volt, the costs associated with the hybrid system should also fall well short of the Volt's costly power train.

The plug-in Prius is a separate model from the all new 2010 Prius Hybrid.  The plug-in version will only be available for fleet service and will not be sold at retail to the general public.

The fleet models will be part of a test bed for Toyota and future development of the plug-in Prius may at some point lead to a consumer model.  The upcoming plug-in Prius will use the traditional nickel metal hydride battery system, but future versions will likely see the addition of a lithium ion battery pack.

The plug-in Prius is expected to launch sometime in 2010.

Source:  Japanese Newspaper Nikkan Jidosha Shimbun