The best selling games of January 25-31 according to Steam, the online retail arm of videogame company Valve, include pre-orders for the new Star Trek Online, BioShock 2, and Battlefield: Bad Company 2 games.

The sales of the original Mass Effect were bouyed by the release of its highly rated sequel. Mass Effect 2 is sitting pretty at both second and fourth positions thanks to its Deluxe Edition having been awarded full marks by reviewers at sites Boomtown, Eurogamer, GamesTM, Giant Bomb and The Onion AV Club among others.

Star Trek Online continues to do well ahead of its official release date on February 2, with full access available from January 30 for those that pre-ordered. Looking slightly further ahead, BioShock 2 is out on February 9. Steam packaged the game's predecessor, BioShock, in with the digital purchase as an incentive to those teetering on the edge.

It's Battlefield: Bad Company 2 that sits atop the sales chart this week, thanks in part to the continued online game access that was made available to customers from January 28 up to its release during the first full week in March. Though the single player mode is said to be much improved over the first Bad Company (which itself wasn't terrible), multiplayer is where it's at and purchasers are getting to play a near-finished version right up until their full copy is available for download.

Top 10 best-selling games on the Steam network, January 25-31
01) Battlefield: Bad Company 2 Limited Edition
02) Mass Effect 2
03) Call of Duty: Modern Warfare 2
04) Mass Effect 2 Digital Deluxe Edition
05) Global Agenda
06) BioShock 2
07) Star Trek Online Digital Deluxe Edition
08) Mass Effect
09) Aliens vs Predator
10) Left 4 Dead 2