A previously developed rigorous theory of diffusion coefficients in liquids is adjusted to practical applications and tested on description of diffusion coefficients in binary non-polar mixtures. The model contains thermodynamic, kinetic, and resistance contributions, the last being based on a new concept: the penetration length. Simple formulae for the penetration lengths are proposed. Comparison to a large set of experimental data shows good performance of the model, which is capable of describing the behavior of diffusion coefficients at different temperatures with the same number of temperature-independent parameters. (c) 2004 Elsevier B.V. All rights reserved.