I once finished Castlevania SoTN in one sitting. Took me almost 17 hours. There's something hypnotizing about Alucard's movement and the game can put you in a trance if you're fully accustomed to the fluid controls

15 hours

Mass Effect 3 26 hours. From Palaven to the end of Rannoch

Me and a friend put easily 40 hours and a bit into halo 3 a few years back.

I think about 20 on a FF12 playthrough once.

I think, for around 35 hours and then one night sleep and continued the next day.
I do it a lot, which is why i am looking for a gamer girl who wanna do the same, like having a game marathon that last for hours and hours.

I am sure i've done a lot of longer ones, but it's so often i've unsure on how many hours i've really played.

But every new game that comes out, i don't stop playing them until i am finished with the game

I don't really know.

I know the longest session that got logged anywhere was Zelda Twilight Princess on Wii at exactly 11 hours about 3 or 4 years ago. Was my third play through (4th if you count GC version playthrough) and I wanted to hurry up and get to the Arbiter's Grounds already. I don't think I ever finished that playthrough though, should be at the Temple of Time or the City in the Sky.

Otherwise I'm pretty sure that isn't my longest time playing a single game. I'm positive I topped that a couple times with a session of SimCity 4, Rollercoaster Tycoon or any of the Total War games. There's no way to know though, sadly.

I know there must be a game that I played for a long time out there but I just can't remember it. Not the name of the game, but which game it was.

22 hours maybe even more

Around 7 hours.