Chart-Track has reportedly revealed that the Xbox 360 version of Valve's Portal 2 was by far the most popular of the three SKUs released.
ShopTo.net claims to have confirmation that Microsoft's machine accounted for 54 per cent of overall sales. PS3 claimed just 35 per cent, despite the fact the SKU is the first and only to include cross-platform compatibility with Steam on both PC and Mac.
There are two things to consider here.
Firstly, the PC version in reality will have claimed far more than 11 per cent of overall sales due to the undoubtedly high number sold digitally over Steam. These numbers have not been released.
It's also possible that the ongoing PSN outage would have forced many to abandon the PS3 version which is still unable to offer either online co-op or Steam log ins.