  We consider the insurance company as a physical system which is immersed in
its environment (the financial market). The insurer company interacts with the
market by exchanging the money through the payments for loss claims and
receiving the premium. Here in the equilibrium state we obtain the premium by
using the canonical ensemble theory, and compare it with the {\it Esscher}
principle, the actuaristic well known formula for premium calculation. We
simulate the case of automobile insurance for quantitative comparison.
