I saw a Carrefour whilst in Cordoba, Spain that was advertising diesel at 1.77 and the station next to it was just over €2 so I went to Carrefour. Filled up and saw that I had paid just over €2 a litre, more expensive than the other garage. Turns out the 1.77 price was for Carrefour card holders! Bugger.
In other areas of Spain I was paying around 1.90 give or take depending on which station I used. I have a discount card for Galp but found with the discount, it was still more expensive than other companies/supermarkets. As mentioned above, slightly more in France.