Harmonic Potentials and energy state populations

Hi All - Let's say I have a potential energy surface with two minima, one higher than the other. We will label the higher minima B and the lower minima A. Each potential well can be approximated as a harmonic potential with force constants kA and kB for wells A and B respectively. How small must kB be in terms of kA in order for that state (higher energy) to be the more likely state at temperature T?