How much does a game have to sell to warrant a sequel?

[De85]

Riachu said:

De85 said:
Enough to make a profit. Since different games have different development costs it varies. For example, Killzone 2 has been estimated as having a 30 million dollar production budget. At 60 dollars per copy, every copy sold beyond a half a million represents profit. If it sells more, which it most likely will given the hype, then you can count on seeing a Killzone 3.

the developer does not get all of the money sold on a copy of a game. I believe the developer usually gets half of the money per copy of the game sold to retail so Killzone 2 will have to sell a million copies to break even if I am right

 I know, i was just trying for the utmost in simplicity.  Killzone just came to mind because it's the only game I've heard estimates for lately.  The basic premise of what I said however is true.  If the developer profits there will be a sequel.