Users have until 2 p.m. PDT on Wednesday, July 17 to sign up for the beta. Those chosen will be notified via email with instructions regarding how to participate.
While gamers accepted into the beta will not need to sign a nondisclosure agreement, Sony reminded gamers that the closed beta is confidential and that all beta test materials may be serial numbered for tracking purposes.
"Disclosure of any part of the beta test materials to any third party, including but not limited to any trade or consumer press, news agency or any competitor of SCEA, will cause significant and irreparable harm to SCEA, the extent of which may be difficult to ascertain," Sony said.
Killzone: Mercenary launches September 17 and uses the same engine as Killzone 3. The single-player campaign to Killzone: Mercenary will feature nine missions that are reportedly each close to an hour long, and the game will include an eight-player multiplayer mode spread across six maps and three gametypes.
For more on Killzone: Mercenary, check out GameSpot's previous coverage.