Despite increasing Soviet investment in its petroleum industry, oil production in USSR declined for the first time in the post-World War II period, from 12.327 million b/d in 1983 to 11.9 million b/d in 1985. Although oil production continued to increase in West Siberia, it was not sufficient to offset declines in the old producing regions west of the Urals. In the same period, however, gas production increased sharply, from 18.9 tcf to 22.6 tcf, due mainly to development of the supergiant Urengoy field in West Siberia. Efficiency of exploration continued to decrease in all petroleum regions except offshore in the southern Caspian Sea. In all these regions, the quality of the exploration prospects worsened-smaller and less productive structures were drilled, the average d pth of drilling increased, and exploration extended into more remote areas.

The main gain in oil reserves was again achieved in West Siberia, although no new fields of a size comparable to older giants in the Middle Ob region were discovered. Because of the lack of prospects in Lower Cretaceous rocks, which have been extremely prolific, exploration was essentially targeted to the deeper and less productive Jurassic and older sections. Most of the newly discovered oil fields in these sections are of small to medium size. Attempts to establish significant oil production in the northern part of the region, beneath giant gas accumulations, again failed. New, apparently large gas fields were found, but they only add to the surfeit of USSR's established gas reserves.

In other petroleum basins of USSR, the best results were obtained in the southern Caspian Sea, offshore of the Azerbaijan Republic. Development and continuing exploration in the giant 28th-of-April oil field, and several other oil discoveries and gas and condensate discoveries, created a basis for steady increases in production in forthcoming years. No significant discoveries were made in other old producing regions, and exploration in the East Siberian frontier was disappointing. A promising new oil field found in the South Turgay trough may represent discovery of a completely new petroleum basin. Its petroleum potential is yet to be evaluated.