  Motivated by the recent interest in quantization of black hole area spectrum,
we consider the area spectrum of Schwarzschild, BTZ, extremal
Reissner-Nordstr\"om, near extremal Schwarzschild-de Sitter, and Kerr black
holes. Based on the proposal by Bekenstein and others that the black hole area
spectrum is discrete and equally spaced, we implement Kunstatter's method to
derive the area spectrum for these black holes. We show that although as
Schwarzschild black hole the spectrum is discrete, it is non equispaced in
general. In the other hand the reduced phase space quantization is another
technique which we discuss here. However there is a discrepancy between the
result of the reduced phase space methodology and quasinormal modes approach
for area spectrum of some black holes.
