China is quickly overtaking the United States as the world's biggest importer of oil. Not only that, but China now buys more crude oil from the Middle East than the US does — a shift that some experts think could have big geopolitical implications in the years ahead.

Roughly half of China's imported oil now comes from the Persian Gulf, whereas America's reliance on Middle Eastern crude has been steadily shrinking in recent years. Here's a good map from Bruce Jones, David Steven, and Emily O'Brien of the Brookings Institution laying out China's situation:

Where China's oil imports come from

China currently imports around 5.6 million barrels of oil per day on net, with about half of those imports coming from the Persian Gulf region. As the map shows, Saudi Arabia, Iran, Oman, and Iraq dominate the list (as do Russia and Angola) — and most of the oil flows through the Strait of Malacca, a vulnerable chokepoint.

The United States, meanwhile, now imports around 5 million barrels per day, and its list is quite different. Only 41 percent of US oil imports now come from the Persian Gulf (mostly from Saudi Arabia). By contrast, more than half of US oil imports come from Canada and Mexico:

Where US oil imports come from:

Why does any of this matter? On one very basic level, where people get their oil isn't overly important. Oil prices tend to rise and fall together all over the world, no matter the source, and an oil spike that crushed China's economy would hurt America's economy too.

China is becoming more dependent on Middle Eastern oil than the US

But as the Brookings paper notes, China is becoming much more directly dependent on Middle Eastern oil than the United States is, and that fact alone could have big implications for geopolitics for the region.

"The United States has long been exposed to the geopolitical risks associated with energy production and transit, but now, increasingly, so too are the Asian powers," the authors write. "Chinese and Indian policymakers are scrambling to understand these risks and to work out how to manage them."

They also note that the impact on the psychology of American policymakers could be profound: "American strategists, meanwhile, may be tempted to fulfill Chinese fears and use energy as a source of pressure on its most significant rival. Others will see an opportunity to disengage from the Middle East during a period of fiscal austerity, leaving Beijing and Delhi to take responsibility for the troubled region." (The Brookings paper argues against both these approaches — see the full piece for more.)

Why China has surpassed the US in oil imports

It's worth noting that China's position as the world's top oil importer is relatively new. For many decades, the United States was the undisputed champion of oil importing. This was basically the one fact that most people knew about US energy policy — that the country was way more dependent on foreign oil than anyone else.

But that's now changing. The Energy Information Administration estimates that China surpassed the US in net oil imports sometime around the fall of 2013:

Part of this is due to China's rapid growth, as more and more people are driving. Part of it is due to the fact that China has been slow to develop its own domestic oil resources. So the country has to seek out petroleum abroad.

But another big factor has been changes in the United States. Thanks to the fracking boom in places like Texas and North Dakota, the US is producing more and more of its own crude oil. At the same time, improvements in fuel efficiency and a slowdown in rates of driving means that the United States is reducing its oil consumption. Add those two together, and imports are dropping.

Further reading: Here's an excellent Wall Street Journal story from last year predicting that China would soon overtake the US as a buyer of Middle Eastern oil.