According to the Chart Track all-formats chart for the week ending August 25, 2K's Bioshock is number one in sales.
With this strong start, Bioshock becomes the second fastest-selling Xbox 360 title, just behind Gears of War.
Activision's Transformers: The Game, which had been at number one since the beginning of August, dropped to the second position.
Dr. Kawashima's Brain Training and More Brain Training with Dr. Kawashima for the DS took third and fourth place, with Wii Play dropping from number two to number five on the chart.
Rounding out the top ten were Pokemon Diamond, Harry Potter and the Order of the Phoenix, Surf's Up, Blue Dragon, and Ghost Recon: Advanced Warfighter 2.
As with Bioshock, Blue Dragon is a new release for the Xbox 360. The only other new release this week is THQ's Moto GP '07 at number 33.
Ghost Recon: AW2 has re-entered the charts on the basis of the release of the PS3 and PSP versions.