Diesel now costs about 5p/ litre more than petrol (gasoline): 86.9p for petrol, 92p for diesel.

http://www.petrolprices.com/

http://www.planetark.org/dailynewsstory.cfm/newsid/38346/story.htm

a diesel car costs about $2500 more.

http://lib.smmt.co.uk/articles/sharedfolder/Publications/ACF22CC.pdf

p11 - diesel percentage of new cars:

UK - 37%
France - 69%
Germany -42%

Hybrid cars were only 6,225 (in 2004).  Alternate Fuel Vehicles (compressed gas) declined sharply due to the end of a tax subsidy scheme.

Diesel cars cost more, but hold their resale value better, than petrol equivalents (people expect greater longevity from the motor -- this, surely, gives a better overall energy equation over the lifetime of the car!)

The high proportion of diesels in France is price-driven. Historically, diesel was about 20% cheaper at the pump than petrol, because of lower tax -- this was originally a subsidy for truckers. The tax difference has been phased out, but diesel remains slightly cheaper (current prices : around 1.05 euros per litre diesel, 1.15 petrol)