The paper presents the results of loading tests conducted on samples of the Ciężkowice sandstones, hydrocarbon collectors within the Outer Carpathians, at variable pressures (P) and temperatures (T), by modeling orogen conditions down to about 3.5 km below the surface. The studies show that the confining pressure (P) and temperature (T) influence the deformation process and the destruction character in the studied rocks. Analysis of differential stress - deformation curves and the distinguished deformation phases have shown that increase of P and T causes a smaller contribution of the compaction phase, a wider range of the elastic deformation and the presence and increase of the stable cracking phase. Non-stable cracking, initiated by the threshold of absolute dilatancy, with increase of pressure and temperature decreases its contribution in the total differential strain (1–3)max with 70% at atmospheric pressure and room temperature to slightly above 10% for P and T corresponding to values at the depth of 3 km below the surface. These changes influence the destruction of the rock material, which from gentle, controlled cracking at low pressures and temperatures passes into rapid, violent destruction at high P and T levels.