The only full-size models that did not recover were lower price models such as the Chevrolet Bel Air and Ford Galaxie 500. Slightly smaller models such as the Oldsmobile Cutlass, Chevrolet Monte Carlo, Ford Thunderbird and various others sold well. Economical imports succeeded alongside heavy, expensive vehicles. In 1976, Toyota sold 346,920 cars (average weight around 2,100 lbs), while Cadillac sold 309,139 cars (average weight around 5,000 lbs). Federal safety standards, such as NHTSA Federal Motor Vehicle Safety Standard 215 (pertaining to safety bumpers), and compacts like the 1974 Mustang I were a prelude to the DOT "downsize" revision of vehicle categories. By 1977, GM's full-sized cars reflected the crisis. By 1979, virtually all "full-size" American cars had shrunk, featuring smaller engines and smaller outside dimensions. Chrysler ended production of their full-sized luxury sedans at the end of the 1981 model year, moving instead to a full front-wheel drive lineup for 1982 (except for the M-body Dodge Diplomat/Plymouth Gran Fury and Chrysler New Yorker Fifth Avenue sedans). OPEC soon lost its preeminent position, and in 1981, its production was surpassed by that of other countries. Additionally, its own member nations were divided. Saudi Arabia, trying to recover market share, increased production, pushing prices down, shrinking or eliminating profits for high-cost producers. The world price, which had peaked during the 1979 energy crisis at nearly $40 per barrel, decreased during the 1980s to less than $10 per barrel. Adjusted for inflation, oil briefly fell back to pre-1973 levels. This "sale" price was a windfall for oil-importing nations, both developing and developed. The embargo encouraged new venues for energy exploration, including Alaska, the North Sea, the Caspian Sea, and the Caucasus. Exploration in the Caspian Basin and Siberia became profitable. Cooperation changed into a far more adversarial relationship as the USSR increased its production. By 1980, the Soviet Union had become the world's largest producer. Part of the decline in prices and economic and geopolitical power of OPEC came from the move to alternative energy sources. OPEC had relied on price inelasticity to maintain high consumption, but had underestimated the extent to which conservation and other sources of supply would eventually reduce demand. Electricity generation from nuclear power and natural gas, home heating from natural gas, and ethanol-blended gasoline all reduced the demand for oil.