The injection of carbon dioxide into coalbeds to increase methane recovery is an emerging technology which was tested in various pilot installations. Carbon dioxide stored in coalbeds is usually in supercritical state and therefore investigation of supercritical adsorption of this gas on coal is a subject of various studies. In the paper impact of three equations of state i.e. Peng Robinson (PR), Soave-Redlich-Kwong (SRK) and the most accurate Span-Wagner, as a reference, on the calculation of sorption capacity was investigated. Langmuir parameters were calculated on the basis of experimental results of CO2 volumetric sorption by a Selar Cornish coal sample. It is concluded that the use of cubic equation of state (PR and SRK) for the calculation of supercritical CO2 sorption on coal gives unreliable results by lowering apparent absolute adsorption in the lower pressure range (< 9 MPa) and unrealistically increasing it at higher pressures.