The problem of comparison of island arc andesites in terms of petrochemical data is examined. It has been proved that in the case of the Kurile Arc, two main factors exist governing the petrochemical variety of andesites. We have made use of original multivariate statistical techniques and computer software to extract these factors. The following interpretation is suggested: the first factor (“mantle” factor) is the depth to the Benioff seismic zone, and the second (“crustal” factor) is supposedly the position of the peripheral magma chamber. Trends in the variations of the initial chemical components depending on changes in the controling factors have been determined. It has also been established that the chemical composition of volcanics depends on the type and structure of the crust.