The BACK equation of state has proved to yield very accurate correlation/prediction of simple compounds and their mixtures. We determined the characteristic parameters of this equation for hydrogen in the broad range of temperatures 40-400 K and pressures up to 50 MPa. Moreover, characteristic parameters of compounds with which hydrogen forms important mixtures, i.e. nitrogen, oxygen, methane and ethane for the temperature range from slightly above T-c up to 400 K and pressures up to 5 MPa are given. In all the cases the theoretical value of the non-sphericity parameter, alpha, was used. (c) 2005 Published by Elsevier B.V.