Valve, creators of best-selling game franchises (such as Half-Life and Counter-Strike) and leading technologies (such as Steam and Source), today announced that outlets worldwide (retailers and Steam) are now accepting pre-order reservations for Portal 2, the epic sequel named the “Most Anticipated Game of 2011” at the Spike TV Video Game Awards.

Special pre-order offers vary at participating outlets around the world and include a variety of dollars off and/or exclusive in-game content for those who reserve the game for purchase before it is released the week of April 18. These include $5 off the full price, exclusive in-game skins for the coop bots (Atlas and P-body), and more. Check your favorite outlet for details.

“Portal 2 is shaping up to be the most innovative title in Valve’s history, and to be a much larger experience than we originally planned,” said Doug Lombardi, vice president of marketing at Valve. “As such, we are aggressively promoting the title with more retail promotions than we have put behind any prior release.”

The highly anticipated sequel to 2007’s Game of the Year, Portal 2 is a hilariously mind-bending adventure that challenges you to use wits over weaponry in a funhouse of diabolical science.

Using a highly experimental portal device, you’ll once again face off against a lethally inventive, power-mad A.I. named GLaDOS. And this time you won’t be alone. Meet an expanded cast of characters as you think your way through dangerous, never-before-seen areas of Aperture Laboratories.

Break the laws of spatial physics in ways you never thought possible, with a wider variety of portal puzzles and an expansive story that spans a single player and co-operative game mode.

Available for the Playstation 3, Xbox 360, PC and Macintosh computers, Portal 2 is scheduled to ship worldwide the week of April 18, 2011. For more information, please visit www.thinkwithportals.com