SINGAPORE — In the eight years of Vladimir Putin's presidency, Russia's energy riches were used as a lever to rebuild the country's influence and power. As his successor, Dimitry Medvedev, took over last week and Putin became prime minister, both leaders will worry about signs that this energy muscle is starting to shrink.

The world should worry too. The first fall in Russian oil output in a decade is adding impetus to the surge in the price of oil, which rose above $120 a barrel to a record high early last week. Russia is a key oil producer and exporter. In recent years it has ranked second, after Saudi Arabia, but has sometimes produced even more oil than the Middle East giant, by far the largest producer in the Organization of Oil Exporting Countries. The OPEC cartel supplies around 40 percent of the 86 million barrels of oil currently used each day around the world.

Japan, China and other leading Asian oil importers will also be concerned at the decline in Russia's oil output. With the eighth-largest proven oil reserves, Russia was considered the most promising oil area outside the Middle East. Rapid production growth for much of the time Putin was president helped to meet booming Chinese demand for oil and limited the rise in oil prices.