The sales for Killzone 3 have been disappointing in its first week, selling only 500K units, which is a third of what Killzone 2 did in its first week of release.
Killzone 2 sold 2.58M units in its lifetime, and considering the budget Sony pumped into 3, it would be a disaster if it only managed to move 860K, if the same ratio continues for 3‘s lifetime. While it’s unlikely Killzone 3 will sell less than 1M, it might not outsell its predecessor.
The original Killzone for the PlayStation 2 sold 760K units.