[en] The momentum transfer cross section for electrons in mercury vapour has been derived over the energy range 0.1-5 eV from the drift velocity data of Elford (1980). The cross section has a resonance at 0.5 eV with a maximum value of 180A²(1.8x10^-18m²) It is shown that previous cross sections derived either from experimental data or obtained by ab initio calculations are incompatible with the drift velocity data