I've played it a few times, using the computers MPG and the trip to calculate how much fuel I have. The Zeds gauge is notorious for reading wrong and even calculating it then adding what I put in comes to less than the full 80 liters, so I assume the MPG reads a little lower than it should also. Not a bad thing.
I did "run out" of petrol once playing this game and ha to coast into a lay-by and call for help My brother arrived with a 5 liter can and the car started flawlessly once it was in, making me think it wasn't actually empty. I then drove about 3 miles to the nearest BP and only got about 70 liters in, meaning there was still 5 in there when it ran out.
My only guess is, it wasn't actually empty, but the petrol is a little dodgy down that low. I'll not be running it that close again incase some crap gets into the engine and causes problems…