Oil shale is currently used for electricity and oil production. The production of the latter produces large quantities of residue, i.e. semi-coke, from which it could be possible to create valuable porous materials with high surface areas. These adsorbents could be used in a wide range of environmental and industrial applications. To produce adsorbents, it is first important to characterise the source material and to find out to what extent the surface area differs depending on the particle size. Considering the above, seventeen oil shale fractions, with particle sizes ranging from 36 µm to 8 mm, were characterised in terms of total organic carbon (TOC) content, specific surface area (SSA) and porosity. Special attention was paid to the analysis of SSA using Brunauer-Emmett-Teller (BET) theory. The SSA of the studied oil shale was found to vary from 4 to 13 m2/g depending on the particle size. The analyses performed supported the known trend that the finer fractions have slightly higher contents of organic matter (i.e. kerogen) as well as higher surface areas. In addition, preliminary pyrolysis tests with the oil shale fractions were also carried out to see the effect of thermal treatment on surface area. After treatment, BET surface areas were in the range of 19–38 m2/g. As the final goal is to obtain activated carbon with a large SSA, it is important to know if and how much the results are affected by the source material. The present study provides fundamental knowledge about the source material that will enable applied research in the future.