Probably about 15 with Civ IV. It was the first and last time I played. I started playing around 4pm, and stopped at 7am. I didn't even realize how much time had gone by until my alarm went off for school.
My friend and I co-oped Resident Evil 5 the day of release for 23 hours straight until we beat it :D
Dude, I beat that in one sitting too. By myself =( Took me like 10 hours I think, Easiest difficulty.
That game is the stuff, but by playing it for so long, I actually got sick of it and haven't played it since.was fun fighting over who deserves what weapon