The Metropolis method of calculating the electron–ion geminate escape probability in high-mobility systems has been applied to determine the initial thermalization distance distribution in several non-polar liquids for agreement with measured free-ion yield. Calculations have been performed for a series of hydrocarbons and other liquids, at room temperature, over the range of electron mobility μ from about 1cm 2 V −1 s −1 to 100cm 2 V −1 s −1 , and for liquid methane over the temperature interval 122–192K (μ=50–800cm 2 V −1 s −1 ). The results clearly confirm inapplicability of the standard Onsager theory of ion recombination to analyze experimental results for high-mobility liquids. The mean thermalization distances determined by the Metropolis method are significantly shorter than those obtained using the Onsager theory. Some regularities in the thermalization distance in various liquids are revealed, which were unobserved in earlier studies because of the use of the Onsager theory. The concepts proposed earlier that the mean thermalization distance in liquids of similar structure is scaled by either the density or the dielectric constant are only partially corroborated.