To celebrate Killzone 3’s one-year anniversary, Guerilla Games will be flipping the double XP switch for the entirety of the weekend.
Double XP will start on Friday, March 2 at 8 a.m. PT and last until Monday, March 5 at 2 a.m. PT. Double XP will not be activated for those playing the free Killzone 3 multiplayer experience (set to be released later tonight).
Source: PS Blog