I see it almost impossible.
This is my extremely best case scenario.
Final Fantasy XIII PS3 --- Japan 2.1M --- US 1.5M --- Europe 1.2M (Total 4.8M)
Final Fantasy XIII Xbox 360 --- US 1.7M --- Europe 0.9M (Total 2.6M)
Total 7.4M
In order to outsell Final Fantasy VII it should have to make these monster and unbelievable sales.
Final Fantasy XIII PS3 --- Japan 2.5M --- US 2M --- Europe 2M (Total 6.5M)
Final Fantasy XIII Xbox 360 --- US 2M --- Europe 1.5M (Total 3.5M)
Total 10M







