3D visualization of internal structure and mineral composition of three major Bazhenov lithotypes identified within the framework of the Provisional Guidance for Oil Reserves Assessment in the Bazhenov Fractured and Fractured-Porous Reservoirs of the West Siberian Petroleum Province Abstract. The paper presents the results of 3D structure, surface micromorphology, and mineral composition visualization of the samples of three major Bazhenov lithotypes identified within the framework of the Provisional Guidance for Oil Reserves Assessment in the Bazhenov Fractured and Fractured-Porous Reservoirs of the West Siberian Petroleum Province. On the results of the work, differences between the major Bazhenov lithotypes are identified with the use of modern methods of core analysis, such as X-ray high-resolution microtomography and scanning electron microscopy. The need to use the high-resolution methods of electron and X-ray microscopy for analysis of core material taken from the Bazhenov Fm is demonstrated. The possibility of operative correction of the focus of prospecting and exploration works and obtaining more correct variables used to estimate reserves is planned.