Whenever there is a quite profitable, logical strategy around, you will always have people saying that it is dead because of the number of guys already doing it. Pair trading has always been around and of course the biggest winning pairs have been exhausted or arbed so much that it is not possible anymore for a retail to be profitable trading it. But if you search deeper, there is always some unconventional pairs to trade. And it can be rewarding. Itmediaco, on the level of correlation needed to create a pair strategy, I think the problem in stocks is that the correlation is quite unstable. Futures correlation are more stable. There are pairs that have 90 % correl for a long time. That is just an impression, no real study.