Tables are given for the second virial coefficient and Joule-Thomson coefficient (at low pressures) of a gas whose molecules are non-polar, approximately cylindrical, and stiff. The tables cover the range of length/breadth ratio consistent with the last assumption. The tables can be used for the analysis of observed virial coefficients of gases whose molecules satisfy these assumptions, and give an estimate of the intermolecular forces between these molecules at any relative orientation. For small ratio of length to breadth the virial coefficient is nearly the same as that of a spherical molecule with certain mean values of the parameters defining the intermolecular field. This makes it possible to relate these mean parameters to the critical constants and to the parachor. The virial coefficients of nine gases are analysed. The data on seven hydrocarbons enable one to estimate the law of force between molecules of the lower non-polar hydrocarbons.