It is an honour and pleasure to write a foreword to this useful and interesting book. Authors are very well known researchers who pioneered percolation modelling of transport in porous media in Russia from the early 80-th till nowadays. The main scope of the work presented in the book was developed when bright papers by A. Aharony, H.T. Davis, F.A.L. Dullien, A.A. Heiba, R.G. Larson, R. Lenormand, M.Sahimi, L.E. Scriven, D. Stauffer, M. Yanuka, Y.C.Yortsos were not available at the "other" side of the Iron Curtain. Nowadays hundreds of works and papers with the "percolation" keywords ap­ pear in petroleum and related applied research areas. The book will take a re­ markable place in the "petroleum percolation" bibliography. There are two important features of novelty in the monograph presented. First of all the authors developed a generalization of percolation clusters theory for grids with varying conductivity. Technique of representation of an infinite cluster as an hierarchial set of trees (so called r-chain model) allows to present conductivity of a stochastic grid in a closed form of explicit formulae. This method differs from those known in the West, such as effective media theory, solutions for the Bethe-lattice, etc. It has his own area of successful appli­ cations.