The best-selling games for January 18-24 according to Steam, the international online retail arm of videogame company Valve, have pre-orders for the science-fiction role playing and action game Mass Effect 2 boosting the title's Deluxe Edition from third ranking up to first place. Battlefield: Bad Company 2 goes straight in to second after being made available for pre-order over the weekend.

In fact, much of the chart is made up of pre-orders, as BioShock 2, Aliens vs Predator, Global Agenda and Star Trek Online contribute to a busy release schedule over the next few weeks.

The developers behind Battlefield: Bad Company 2, Global Agenda and Star Trek Online are all offering a pre-release version for purchasers to try prior to the finished games' scheduled releases.

Company of Heroes shoots in to seventh after a cut-price weekend promotion, and there are still two big 2009 PC games that haven't been dislodged from the top 10 yet: Modern Warfare 2 hangs in at fourth and Left 4 Dead 2 refuses to accept banishment.

Top 10 best-selling PC games on the Steam network, January 18-24
01) Mass Effect 2 Digital Deluxe Edition
02) Battlefield: Bad Company 2 Limited Edition
03) BioShock 2
04) Call of Duty: Modern Warfare 2
05) Aliens vs Predator
06) Mass Effect 2
07) Company of Heroes Complete Pack
08) Global Agenda
09) Star Trek Online Digital Deluxe Edition
10) Left 4 Dead 2