(FORTUNE Magazine) – In the largest judgment against an oil company for violating price controls during the 1970s, a Washington federal appeals court ruled that Exxon must pay the U.S. government $900 million for overcharging customers, plus $1 billion in accumulated interest. The money will be distributed to states for energy conservation programs. Under price controls, oil produced at 1972 levels had to be sold for as little as $5.75, while new oil, defined as that amount of oil produced in excess of 1972 levels, could be sold for more than twice as much. Some other categories of oil weren't controlled at all. Energy Department officials claim that Exxon lumped the total production from a large Texas oil field under fewer of its leases, making most of the field's production ''new oil.'' Exxon officials say that the government regulations were unclear and that it will petition the Supreme Court. A reversal seems unlikely. In February the Supreme Court let stand another appeals court decision that ordered Getty Oil to pay $133 million for violating price controls. Nearly 450 other price- control cases are pending. The overcharges could add up to more than $4 billion, a real gusher for the government, even if it must reimburse $1 billion to $2 billion in taxes that the companies paid on profits they shouldn't have reaped.