27 hours playing a MUD a very long time ago called Dragon Realms.  This was only with bathroom breaks (had food in my mini fridge).  If you want to go further, I went up to almost 48 hours before I passed out.

Paid for a 2/3 day? (been a very long time) quest and I wanted to get as much out of it as possible.

Some of you guys posting 30+ hours make me wonder what kind of chemical assistance you had..

16 hours...Super Metroid. Beat it the first night I rented it.

As far as I know, there is no way to get permanently stuck in Water Temple. There's always, ALWAYS, another key within reach, even when you think you spent a key at a "wrong" door. It's just complicated at times. Unless you know something I don't.

This is one breakdown of how you can't get stuck. breakingzelda.blogspot.com/2013/03/the-water-temple-myth-part-1.html

But well, on topic. The longest session I've had was either Brawl or Gran Turismo 5. Probably Brawl but I remember I threw an intense GT5 "launch party" with some friends and hooked up several PS3's to play. This was at launch, before none of us had any chance to see how bad it was (not really bad but nothing new either). Still fun ofc.

About 8 hours on Quantum of solace on xbox360 from 10pm to 6am the next day. The online multiplayer was so addictive

10-15 hours

mhm.... okay. I guess I just missed a key. lol I guess I wasted some time there, but thankfully, another myth busted. I didn't have big problems with the Water Temple since, but I thought it was because I was playing the GC version and 3D remake. I've heard some people claim, that Nintendo had fixed the issue on those versions.

Should have known because it always seemed kinda fishy :/

Whatever, thanks for the enlightenment :D

Years and years at a time. The game is called life, and you're all playing it.

8-10 hours with Smash Bros U! My friend and I had a blast playing Smash that night!

6-7 hours.

Happened once with Bayonetta 2, and about 3 times with AC IV Black Flag. So many side things to do!!! :3

21 hours of WWE: Day of Reckoning. I didn't yet have a memory card for my Gamecube, and leaving the console on indefinitely isn't an option in Nigeria. The power supply isn't constant. Its erratic. So one day when the power was just restored, I had a feeling it would stay on for at least 24 hours straight. I played the story mode of DoR from 10am of that day to 7am of the following day.
I beat the story mode, woke my brothers up to go play with all the things I had unlocked, then crashed. They later told me the power went sometime between 10 and 11am that morning.