  In this survey we study the OSV conjecture for 4D N=2 extremal black holes of
type IIB suprstring theory. We apply T-duality to find the generalized
prepotential of the low energy limit of this superstring theory up to one-loop
order in the closed string coupling. On the other hand, we calculate the
tree-level and one-loop free energies of B-model topological string theory. To
compare them we will explicitly show that the OSV conjecture holds for type IIB
N=2 extremal black holes.
