I get over 50 mpg from my diesel Citroen, doesn't alter the pain in the wallet when it needs fuel! I need to put about 60 litres in at the moment, so that'll be nearly £85 worth. I've got my useage down so that that'll last me 6 weeks, but it's still nearly £750 a year. I'm trying to get bikes and walking to take up some more of the miles but there's a limit to how far that process can go.
With servicing, VED, insurance and so on the actual running cost is at least double that - roll on the day when we can sensibly get rid of one car!