Over half of all boxed Portal 2 sales in the UK last week came on Microsoft's Xbox 360, according to GfK-ChartTrack data.
Just 35 percent of sales were of the PS3 version of the game - something of a surprise considering the cross-platform capability offered with the title's Steam features.
The news comes as PSN suffers a sixth day of downtime following an "external intrusion" of the service.
54 percent of sales came on Xbox 360, with a further 10 per cent buying the boxed version of the PC game.
However, GfK-ChartTrack's figures do not take into account the number of sales made via Steam.
Portal 2 was sold early on Valve's digital distribution network as a reward for fans who purchased a 'Potato Sack' of indie titles.