Rock pore space is a rock mass composed of a large number of irregularly arranged and shaped pores. The diameter of the pores and their distribution and tortuosity determine the possibility of collecting and conducting reservoir fluids (Oil, Natural Gas and Saline water). Characterization of the pore space is intended to determine the distribution and size of the cavities in the rock. The characteristics of the study is based on parameters such as porosity and permeability and upon which the petrophysical static model is built. The article discusses methods of mercury porosimetry from the aspect of the exploration of the pore space of reservoir rocks for hydrocarbons. The research results of the petrophysical parameters of samples similar to typical reservoir rocks and unconventional rocks were presented. The results of capillary pressure tests in graphic form for six samples of the Inoceramian sandstone of the Skole unit were also given. The results of the petrophysical studies show the limitations of the use of the mercury porosimetry method in investigations of low reservoir parameters. Therefore, the authors have identified the next stage of research as exploring the application of the helium porosimetry method due to the chemical neutrality of helium and its small particle size.