According to Rod Fergusson, executive producer on Gears of War 3, four player co-op has not been possible before the third game in the series.
"Well, there's a reason it took until Gears 3 to do it." Fergusson explains in the September issue of Edge. "There are so many challenges in trying to accommodate four players, especially the way we do it. We didn't want to do an army of clones; we wanted to do story relevant characters."
"And so as soon as you're going to do four player co-op in the Gears world with story relevant characters, it's a real challenge just from the narrative side. Basically, nobody goes through anything alone - they always have three witnesses."
"And beyond that, you have to think: 'OK, we're going to have four people running around, and they all want to take cover and they all want to flank'. It really causes you to have to open up the environment, and create room, and make sure all those things are available to that number of players.
"We've gone back to that Gears 1 approach to what we call 'combat bowls'. Here's a play space that's big enough, and you can go explore it and do whatever you want to do because there's room for you to do it. With four people, you can't really restrict their movement too much."
Gears of War 3 is due for release September 20, for Xbox 360.