In 1956, Marion King Hubbert, a prominent geologist for what is now Royal Dutch Shell (NYSE: RDS-A  ) , made a bold prediction. Based on an extensive analysis of reserves and production data, he concluded that U.S. crude oil production would peak at some point in the late 1960s or early 1970s, after which it would begin an inexorable decline.

For decades, his dire prediction looked startlingly accurate. In 1970, U.S. oil production reached 9.6 million barrels a day -- a level that hasn't been equaled since -- and then began to decline. It fell steadily from 1970 to 1976, and then rose modestly until 1985, after which it once again slipped into a steady decline that lasted for more than two decades.

Hubbert's prediction laid the path for what has since become known as peak oil theory, a highly influential theory that argues that global oil production is rapidly approaching, or has already reached, a peak. Some advocates of the theory even warn that once oil runs out, chaos will ensue, leading to "war, starvation, economic recession" and perhaps "even the extinction of homo sapiens."

A line of cars at a gas station in Maryland in June 1979. Photo Credit: Wikimedia Commons.

But then something happened that almost no one had predicted. Starting in 2008, U.S. crude oil production began to grow, slowly at first and then much more rapidly after 2011. Last year, it averaged nearly 7.5 million barrels per day, the highest level since 1989, and recently reached 8.43 million barrels per day, a level not seen since October 1986. So what happened?

How technology changed the game
At the risk of oversimplifying, technology happened. Specifically, the widespread application of advanced drilling techniques, including horizontal drilling and hydraulic fracturing, allowed energy companies to tap vast deposits of oil and natural gas buried in shale formations thousands of feet below the ground.

Not only have technological improvements boosted U.S. crude oil production to levels not seen since the 1980s, but they've also helped boost crude oil reserves to their highest level since the 1970s. As of the beginning of 2013, U.S. proven crude oil reserves stood at 30.5 billion barrels. That represents an increase of 11.5 billion barrels, or 60%, from year-end 2008 levels, even as 8.4 billion barrels were produced over that time period.

Proven reserves are defined as those that can be economically extracted at current prices using existing technology with a reasonable degree of certainty, meaning a probability of at least 90%. The reason proven reserves have increased so sharply is a combination of new discoveries, more thorough appraisals of existing fields, and technological improvements that have improved recovery rates.

Shale resource potential continues to grow
Take North Dakota's Bakken shale, for instance, one of the largest shale oil discoveries in North America. As operators have improved their drilling techniques in the Bakken over the past few years, they've opened up an entirely new play called the Three Forks formation -- a deeper, separate formation that rests directly below the Bakken and extends much further out into parts of Montana and South Dakota.

An oil rig in North Dakota's Bakken shale. Photo credit: Ole Jorgen Bratland / Statoil ASA.

As a result, total reserves for the Bakken/Three Forks are now estimated to be almost 900 billion barrels, up from roughly 570 billion barrels in 2010. While only about 3.5% of this oil is currently thought to be recoverable, technological advances could drive that percentage significantly higher. Already, improvements in drilling efficiency and smarter well completion methods have allowed several Bakken operators to coax much more oil and gas from their wells.

For instance, Continental Resources (NYSE: CLR  ) , the leading Bakken driller, has seen tremendous initial success from testing tighter spacing between its wells. The company recently drilled 14 horizontal wells spaced 1,320 feet apart in the in the southern part of its Three Forks acreage that produced 50% more oil and gas in their first three months of production than the company's average Bakken well.

This technique of spacing wells closer together -- known as downspacing -- is also yielding encouraging results for Kodiak Oil & Gas (NYSE: KOG  ) , another Bakken driller that's currently evaluating 800-foot spacing and 600- to 650-foot spacing between wellbores as part of its Polar Pilot projects. Initial results from these pilot programs suggest that the company will be able to unlock additional drilling locations through tighter-density drilling without interfering with existing wells.

Is peak oil theory still relevant?
As these examples highlight, continued improvements in drilling technology have allowed energy companies to tap previously unreachable shale formations, resulting in a sharp increase in production and reserves. In the years ahead, operators may turn to enhanced recovery methods such as carbon dioxide injections to boost recovery rates even further.

Still, I don't think these developments render peak oil theory irrelevant. Even though technology has unlocked vast new reserves, fossil fuels are finite resources, after all, and will eventually run out. Technological improvements can merely extend the amount of time before that happens. Eventually, though, there's no denying that we must wean ourselves off fossil fuels.