PSA (PSA Peugeot Citroen) together with Bosch has came out with a unique concept of hybrid vehicle which is partially powered by compressed air compare to the current trend of partial electric. This hybrid air is being developed together with Bosch and is said to be able to offer more than 80 miles per gallon. This technology will include a hydraulic pump that would run in all-gasolin, all-air or hybrid modes.
The idea to pursue this direction is due to the weight as Air is definitely much lighter that battery. Also it might just be more cost effective in the long run to maintain the compressor then the battery life.
PSA hopes that this hybrid concept will find its way to the production of Peugeot and Citroen subcompact models by 2016.