Actually, I've just found this site, with over 8000 petrol stations in France and their current prices for Diesel, SP95, LPG and something else that I've never heard of, and found SP95 at the Port Grimaud Elf station is 1.46 euros and the Carrefour is 1.5 euros - what a great site!
But it's not pro rata. When detax was 60cents, taxed was about 1.20. Hence the tax is about 60cents. With the oil price rise the tax remains 60cents or so, hence taxed is now less than 2x untaxed, if you get my drift. I think!