User blog comment:Ab517/Season 4 hope/@comment-67.62.189.6-20150624124434

There are definitely a lot of hints for a fourth season. That said, I can't even say for sure what that season will cover. Given how much time they spent addressing Issei and Rias's relationship this season, much of volume 10, minus the rating game, would be redundant. And with the debut of Welsh Blaster Bishop, all that's left to do for volume 9 is introduce the hero faction and the school trip (the latter of which they may skip).

In short, if they do make a fourth season, I would not be surprised if they try to cover all the way to volume 12 in one season.