In the present study we used some equilibrium experimental data reported by Mammon et al. (Geophysical Research Letters, Vol. 8, No. 2, pp. 140-142) to investigate effect of high pressure up 65 GPa on bulk modulus calcium oxide (CaO) material. We Vinet’s equation state (EOS) model. The fit as a function p obeys 2nd order polynomial expression: B = 115.37 + 3.84 - 7.25 x 10-3 p2 (where both and ...