The notion of "peak oil" has been thoroughly debunked.

Repeated predictions of the world's oil shortage in coming years simply failed to account for our ability to tap into deeper, more complex seams of energy, buried under the ocean floor or the Arctic tundra. It may become more expensive to get at those new pockets of oil, but it's hard to see how we'll run out of "black gold."

And frankly, the whole discussion is becoming moot -- because our global need for oil is about to peak and eventually decline. As that happens, the economics of the entire energy sector are set to change radically.

No More Super-Spikes
Just five years ago, the global economy was deeply shaken by a huge spike in oil prices. China's rising demand led to fears that oil supplies simply couldn't keep up with an inexorable rise in demand.

To be sure, emerging market economies such as China and India continue to expand. As a result, their oil consumption is expected to keep rising. Yet the rate of growth will sharply slow. For example, China's government policies now aim to boost demand for more efficient cars, electricity-aided buses, while tougher building design codes and a raft of other efficiency gains also blunt the country's energy growth.

Yet in the rest of the world, these dynamics are already playing out, which explains why oil demand is about to peak. Here are some quick examples:

• In the Middle East, plans are afoot to switch power plants from oil to natural gas, leading analysts at Citigroup to forecast that the region will consumer two million less barrels of oil per day by the end of the decade.

• Here in the U.S., the fuel mileage of new cars is increasing by 3% to 4% annually. According to the University of Michigan, the average new car now gets more than 30 miles per gallon. That's up from 25.6 miles per gallon in August, 2008.

• The global plastics industry is quickly transitioning from expensive crude oil to cheaper natural gas.

• LED light bulb adoption is set to steadily reduce household electricity consumption, especially now that GE (NYSE: GE) is making a big push.

• Ships, trains and trucks are also starting the slow conversion away from diesel power and toward liquefied natural gas.

It's easy to chalk this up to the natural gas revolution seen here in the U.S., but energy efficiency should get even more credit. The U.S., which still accounts for 25% of global GDP, is a great example. From 1950 to 2000, U.S. per capita income rose more than 200% while our energy use rose just 50%. Since 2000, our per capita income has continued to rise, but our energy use per capita has actually begun falling.

Look for these trends to continue. According to the U.S. Energy Information Administration. our nation's "energy intensity" is on the cusp of a steady decline. Key highlights from this report include:

• Energy used per household is expected to decline about 27% from 2005 to 2040.

• Commercial energy intensity (defined as energy used per square foot of commercial floorspace) will decline about 17% from 2005 to 2040.

• Industrial sector energy intensity will decrease 25% below its 2005 level in 2040.

• Automotive energy intensity is projected to decline by more than 47% by 2040 from the 2005 value

When Will Demand Peak?
All of the demand drivers noted above are set to play out over the next half decade, but global oil demand will keep rising in the very near-term. The International Energy Agency, for example, expects the world to consumer 92 million barrels of oil per day in 2014, which would be 1.1% higher than the 90.9 million barrels per day this year. Note that the forecast comes in tandem with expected global GDP growth of 3.8%.

Though global GDP will presumably expand 3% to 4% in 2015, those gains noted above will likely push the growth of oil demand to less than 1%. By 2016, we may be looking at the peak, as energy efficiency steps and the rising consumption of natural gas start to have a deeper effect on crude oil demand.

Citigroup analysts have assessed the impact of energy efficiency and the substitution effect from natural gas, and see the oil demand peak coming in 2016.

Winners And Losers
The notion of a demand peak is already having an effect on the oil industry. Major oil producers are already starting to walk away from any new projects that entail high production costs or elevated political risk.

Oil giant ConocoPhillips (NYSE: COP) is a prime example. The company's revenues are expected to fall $7.5 billion this year (to $54.5 billion), in part due to declining production at existing energy fields. Of equal concern is the how the company would fare if oil prices settled into the $80 to $90 per barrel range, as Citigroup anticipates.

In the second quarter, ConocoPhillips earned roughly $13.80 per barrel of oil produced, with an average selling price of $100.14 per barrel, according to Merrill Lynch. That profit margin would be virtually wiped out if oil prices drop 15%.

One of ConocoPhillips' biggest problems: an inability to find low-cost sources of oil. Merrill Lynch, which rates shares as "underperform," notes that the company is "substantially more capital intensive versus peers," meaning it needs to spend more money to get at every barrel of oil it controls.

You could cite similar concerns for any of the oil-focused global energy firms such as ExxonMobil (NYSE: XOM) and Chevron (NYSE: CVX). They are so large that they must scramble to simply to maintain output as existing oil fields deplete. And they are likely to be poor profit generators if oil demand peaks and oil prices settle in below $90.

That sets the stage for Big Oil to be viewed in the same light as Big Tobacco, as the operations are run to optimize cash flow in the face of material revenue headwinds.

Of course, many smaller oil producers will still prosper in the years ahead -- if they have managed to secure low-cost sources of oil and gas. The costs to produce oil vary by region. According to research firm IHS:

• Canadian oil sands require a price of $81 per barrel.

• For an onshore U.S. field, it's $70 per barrel, (though the range is between $45 and $95 per barrel, depending on the rate of oil flow).

• In the Gulf of Mexico, it's $63 per barrel.

• In the Middle East, just $23 per barrel.

That's why it's crucial to analyze the production base for any oil drilling firm you seek to invest in. Many firms that had been focused on shale gas have inadvertently prospered, as those gas wells also contain a prodigious amount of oil and gas liquids. EOG Reources (NYSE: EOG) and Continental Resources (NYSE: CLR) are two clear examples.

The Winners
Of course, the changing global energy picture is producing clear winners as well. On the energy efficiency front, I profiled the macro backdrop in this article and focused on companies that stand to benefit in this article.

Yet we've also extensively covered the opportunities emerging in natural gas. Roughly a year ago, my colleague Joseph Hogue took a broad look at the global natural gas picture.

For a deeper look at the ways to profit from the global shift toward natural gas and away from crude oil, you can check out my comprehensive special report from earlier this year.

The Consumer Angle
Of course, the other clear beneficiary of a peak in oil demand, and subsequent pullback in oil prices, would be the U.S. consumer. According to Deutsche Bank, every 1-cent drop in gasoline prices puts $1 billion more in consumers' pockets.

And a 1-cent move in jet fuel prices affects that industry's profits by $175 million, according to Airlines.org.

Indeed, many industries are ramping up U.S. production as our energy prices (thanks in part of our natural gas boom) are lower than prices found in Europe and Asia. With oil prices poised to settle into the $80 to $90 range, and our ability to pump out higher amounts of gas and oil from the shale plays, the U.S. economy has much more to gain than the top-heavy oil producers have to lose.

Risks to Consider: As an upside risk to the peak oil theory, accelerating global GDP growth in the middle of this decade would likely lead to the peak in demand being pushed back until 2017 or 2018.

Action to Take --> The supply and demand factors affecting oil and gas prices are truly monumental. This is a sector in deep flux, in you need to drop all of your long-held assumptions and brush up on the myriad changes set to take place over the next half decade.