The poorly cemented Ciężkowice poorly sorted sandstone and the compact Mucharz fine grain sandstone have been laboratory tested at the triaxial compressing conditions in thermo-pressurized chamber of a rigid press MTS-815. The confining pressure: P = σ₂ = gσ₃ range from 0 to 96 MPa and the temperature: T from 22°C to 120°C (simulated 500 m intervals from the surface to the depth of 3500 m). During (the) each test, the characteristics of deformation and the elastic wave velocity paths were simultaneously monitored. The volume density and longitudinal wave velocity showed a non-linear increase with the progress of simulated depth, a volume density growth by 1.6 to 4.0%, and the elastic wave velocity up to 250% of the primary value (surface condition), dependable on loading path, phase of deformation, and varying type of lithology. That may lead to wide error margin in a determination of rock’s engineering properties and also create discrepancies between the static parameters of rocks (Est, gνst) determined by standard laboratory load tests, and the dynamic parameters (Ed, νd) determined from the wave velocity and volume density.