We have developed a Lower Palaeozoic petroleum systems analysis in the selected zones of the Polish section of the Baltic Basin (onshore and offshore), which we carried out to assess the potential of shale rock formations as unconventional reservoirs. The areas of the Baltic Basin, which we analyzed represent a diversity of shale formations burial depths and thus different advancement of sediments compaction and organic matter transformation. Methods of dynamic petroleum systems modeling were applied with a 3D modeling workflow (PetroMod suite software). We considered an extensive array of data, including results of geochemical and petrophysical laboratory measurements, geophysical borehole data and, in selected locations — 3D seismic data. Five potentially perspective shale rock intervals (Silurian , Ordovician , and Upper Cambrian ) are identified and interpreted in terms of their geochemical and petrophysical properties. We calibrated the petroleum system models in terms of proper reproduction of diagenetic processes (pore pressure and porosity), thermal conditions (vitrinite reflectance, temperature), and kerogen kinetic model (organic matter transformation ratio, types of hydrocarbons generated). The results of the petroleum system simulations reveal that for the predominant part of the analyzed area, the achieved level of kerogen thermal maturity determines the generation of liquid hydrocarbons, which results in the present-day saturation of shale formations mainly with crude oil. We concluded that the highest generation yields as well as present-day hydrocarbons in place are observed for Ordovician Sasino Formation (onshore and offshore), Silurian/Llandovery Jantar member (onshore), and Upper Cambrian (alum shales) formation. Furthermore, a significant variation in the mass/volumes of accumulated hydrocarbons is observed within each of the shale formations being considered.