The battle for the FPS exclusives rages on this month, as 20-month old Halo 3 outsells Killzone 2 in the US.
According to sales data collected by Gamasutra, Killzone 2 sold 58,000 in the States last month, but it points out that "Halo 3 and Halo Wars each sold somewhere between 57,000 and 74,000 units."
That means that Halo 3 likely topped the 58,000 units mustered by Killzone 2 in April. But there's a small chance it didn't.
Halo 3 was released in late September 2007, so Microsoft is bound to be pleased that it's still making numbers this far from release. The large amount of downloadable content it's received has obviously helped.