In the present stage, most large refineries in the USSR are generally using as feedstock a mixture of several crudes that differ substantially from each other in physical and chemical properties, these crudes coming into the mix in unregulated, arbitrarily varying proportions.

This trend is also typical of other refineries of the country. Meanwhile, the promising oil production regions (West and East Siberia, Mangyshlak, etc.) are characterized by a relatively low demity of consumers of petroleum products. The net result of the interaction between these two tendencies is a considerable breakdown of the previons specialization of refineries in the me of crudes from nearby fields; instead, the refineries have in essence become consumers of mixtures of various crudes that are pipelined from various oil fields. However, the growing inconstancy in quality of refinery-deliver ed crude oil cannot be explained solely on the basis of the increase in number of types of crude used in processing. To a still greater degree, the variations in crude oil quality are determined by the fact that each type of crude oil actually includes crudes from a large group of fields with very substantial differences in physical and chemical properties. In this connection, the data on the Ufa refineries are quite characteristic. During 19701 crude oil entering the branch laboratory of the NovoUfa Petroleum Refinery represented a mixture of seven different types, consisting of crudes from 23 fields; for the Ufa petroleum Refinery, there were eight types of crudes from 18 fields; and for the Twenty-second Party Congress Ufa Petroleum Refinery, seven types from 23 fields. The physicochemical properties of the crudes entering the refineries showed the following ranges of variation: