The simple P-V relation V-x(P, T) = V-x(P-0, T)/[A(x){P + P-x(T)}(mx)] and T-V relation ln T = C[{V-x(P, T)-V(P, 0)}/V-x(P, T)](nx) derived in previous works have been used to calculate the compressibility and thermal expansion coefficient by beta(T) = m(x)/{P + P-x(T)} and alpha(p) = {V-x(P, T) - V(P, 0)}/{V(P, 0)n(x) T ln T}. The subscript x means a state of material such as x = g for glass state and x = l for liquid state, m(x), A(x) and n(x) are constants and P-x(T) is a function of temperature. The V-x(P-0, T) is the specific volume at constant pressure P-0 and temperature T, and V(P, 0) is the specific volume at pressure P and absolute zero temperature 0 K. The values of m(x) for 18 amorphous polymers range from 0.0744 to 0.1382, with an average <(m)over bar (g)> = 0.1101 in the glass state and from 0.0709 to 0.1190 with an average <(m)over bar (t)>; = 0.0953 in the liquid state. The values of n(x) for the polymers range from 0.0214 to 0.4526 with an average value <(n)over bar (g)> = 0.1145 in the glass state and from 0.0283 to 0.8700 with an average value <(n)over bar (l)> = 0.1947 in the liquid state. Values of gamma(V) have the maximum point against temperature at glass transition temperature (T-g) at which P-x(T) decreases rapidly by 1-4 kbar. The Ehrenfest equation at T-g has been examined based on the experimental data of Delta beta and Delta alpha at T-g, and it is found that dT(g)/dP not equal Delta beta/Delta alpha for seven polymers.