"There is little doubt that China's growing consumption changes what ability we have to control our own destiny within global energy markets," said David Pumphrey, a senior fellow at the Center for Strategic and International Studies. "China can now demand a large space inside any energy-policy tent."

China's rapidly expanding need for energy promises to have major geopolitical implications as it hunts for ways to satisfy its needs. Already, China's rising imports have changed global geopolitics. Chinese oil and coal companies have been looking overseas in their quest to secure energy supplies, pitching the Chinese flag in places like Sudan, which Western companies had largely abandoned under international pressure.

The most ambitious effort to secure overseas energy supplies was the failed 2005 attempt Cnooc Ltd. to take over California-based Unocal in an $18 billion bid, which was trumped by politics and rival Chevron. Despite a short pullback in the aftermath of that failed deal, Chinese companies have expanded overseas, buying assets in Central Asia, Africa, South America, Canada and even small stakes in the Gulf of Mexico, with access to cheap credit through China's state-owned banks.

Voracious energy demand also helps explain why China -- which gets most of its electricity from coal, the most polluting of fossil fuels -- passed the U.S. in 2007 as the world's largest emitter of carbon-dioxide emissions and other greenhouse gases.

In the past, being the world's biggest consumer of fossil fuels went hand in hand with being its dominant economy. The question now is whether this will hold true in the future, as nations compete to develop new ways to produce more wealth with less energy. While China is No. 1 in consumption, the U.S. remains the world's biggest economy.

The U.S. is also by far the biggest per-capita energy consumer, with the average American burning five times as much energy annually as the average Chinese citizen, said Mr. Birol.

The U.S. also remains the biggest oil consumer by a wide margin, going through roughly 19 million barrels a day on average. China, at about 9.2 million barrels a day, runs a distant second. But many oil analysts believe U.S. crude demand has peaked or is unlikely to grow much in coming years, because of improved energy efficiency and more stringent vehicle fuel-efficiency regulations.

China's rise is also helping shift the focus for producers in the Organization of Petroleum Exporting Countries. Key OPEC states like Saudi Arabia long looked to U.S. oil consumption for guidance in adding new pumping capacity. But in recent years, OPEC states have built or started building refineries and storage facilities in Asia. Saudi Arabia, the world's biggest crude exporter, now ships more to China than to the U.S.

Prior to the global economic crisis, China had been expected to become the biggest energy consumer in about five years. Economic malaise and energy-efficiency programs in the U.S. brought forward the date, Mr. Birol said.

The decreased "energy intensity" of the U.S. economy is a key reason energy investors, such as General Electric, have increasingly looked to China. Mr. Birol said China requires total energy investments of some $4 trillion over the next 20 years to keep feeding its economy and avoid power blackouts and fuel shortages.