The second-order elastic stiffness tensor and isotropic moduli of -octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (-HMX, P2(1)/n space group setting) on the 0K isotherm are presented for hydrostatic pressures between 10(-4)GPa and 30GPa. The results were obtained from molecular statics simulations using a validated all-atom flexible-molecule force field. Comparisons to previous experimental and computational determinations are provided.