Willie Sutton robbed banks because that’s where the money is. And oil companies venture into deep waters for exploration because that’s where the oil is.

That’s why — even though President Obama had hoped to impose a six-month moratorium on deep-water exploration drilling in the Gulf of Mexico — the oil and gas industry is going to be back. And it’s why in other countries, the deep-water search hasn’t stopped.

Within five years, global deep-water production is expected to rise by two-thirds, to 10 million barrels a day, according to Cambridge Energy Research Associates. That’s equivalent to the amount of crude oil that the world’s largest exporter, Saudi Arabia, produces. And in the United States, improved technology for extracting oil from deep water accounted for about 70 percent of the increase in the U.S. Geological Survey’s estimates of recoverable U.S. oil reserves in recent years.

Those big stakes explain why the oil industry is worried about Obama’s moratorium, which has idled 33 deep-water drilling rigs in the gulf. Interior Secretary Ken Salazar has described the moratorium as hitting “the pause button,” but oil service firms — and Gulf Coast politicians — want the government to hit the play button again.

The Gulf of Mexico, in fact, is very attractive to oil companies set up to drill deep.

First, the sediments are familiar because they resemble layers of rock that stretch onto land or into shallow areas where companies have drilled before. Second, more than a century of drilling has turned the continental United States into a pin cushion, but the deep-water gulf isn’t full of holes. So the chances of finding big reservoirs is much greater in the deep-water gulf.

“While the oil and gas fields of the Appalachian Basin are mostly ‘mature’ (major new discoveries are generally a thing of the past), the Gulf Coast of Mississippi, Alabama and far western Florida continues to have new discoveries,” said a 2001 U.S. Geological Survey report.

According to BP’s drilling permit, the company was targeting a reservoir in rock formed during the Miocene age 5.3 million to 23 million years ago.

In 1999, one company found a field with an estimated 1 billion to 3 billion barrels of oil 155 miles south of Mississippi. The field, known as Thunder Horse is developed by BP.

Even bigger offshore reserves are being found elsewhere. Off the coast of Brazil, the recent discoveries of 10 giant oil fields below a thick layer of salt might have boosted global resources by at least 25 billion barrels.

The Gulf of Mexico and wells off Brazil, Nigeria and Angola produce 80 percent of the world’s deep-water oil

In Brazil, environment minister Izabella Teixeira says: “Today the most important production is from offshore areas.”