About 8 hours, playing GTA San Andreas. Didn't sleep that day. Had fun though.
Ah, to be young... I kinda miss the lack of responsabilities of those days. I can barely fit 8 hours of gaming in a week, let alone a single session.

back in 1999 some friends of mine and me did set up the official world record for a gaming session (72 hours), sadly it was broken very soon tho.

1hr, Revelations 2012.

20 hours, Hearts of Iron II.

12 and a half hours. Completed Age of Mythology and Titans expansion!

Mine was with Terraria for almost 40 hours straight. We (4 guys in total) bought it for a mini lan, and we played the shit out of it. Never played it after that

This is how most of you will die.

24 hours porn

about 30 hours playing NFS carbon on PS2

Current record for me was 68 hours and that was for the release of battlefield 2142. It was at a local lan center they were holding an alienware event and I really enjoyed it for the time I played it. Took breaks every so often to pee, smoke, eat, drink, and a half hour trip home for a shower.

I think mine was between 14-16 hours when Gta 4 came out. The aim was to pass it on launch day and I succeeded =]

4 full days TF2. (idling counts, right?)

Back in uni when Baldur's Gate 2 came out, I think I did something close to 30-ish hours on my first playthrough before falling into a 20-ish hour sleep (with a few bathroom and food/coffee refill breaks in between, if they count) :).

Probably around 12 hours, completing all of Dead Rising 2 with a friend. First time for him, 3rd playthrough for me.

12 minutes angry birds

i think something with 6-7 hours

I've had a few 12+ hours sessions with Civilization.

15 hours fallout 3.

Waaaaay back in the day me and my bro had a two day session on Phantasy Star Online. Certainly haven't done anything remotely close to that since then though.

3-4 hours, but usually i take a brake after 2 hour

3 hours

24 full hours of Scrabble, I think my brain is just that now.

one long ass nazi zombies game, from the morning until late late at night

Around 10 hours of Counter Strike 1.6

24 hours of Dota 2 for charity.