The accuracy of truncated virial EoS to represent pure gas properties was studied in detail for the residual properties (Z - 1), ln phi and (H-R/RT). The Leiden or density expansion was examined with truncation after the second virial coefficient B and also after the third virial coefficient C and compared with the same truncation of the Berlin or pressure expansion. First a Lennard-Jones gas was studied followed by the real gases of methane, carbon dioxide and steam. The results showed conclusively the superiority of the Leiden form, whether above or below the critical temperature. Moreover, the Leiden truncation after B was competitive with the Berlin truncation after C. Tends were further noted in that the enthalpy residual is especially partial to Leiden form in comparison to the compressibility factor and fugacity coefficient, whereas Berlin forms appear to gain some improvement with molecular complexity. (C) 2003 Elsevier Science B.V. All rights reserved.