Oil prices have fallen 70% since hitting a record $147.27 a barrel in July, which means in just five months, crude has given up all the price gains it made in the past four years.

After such a wrenching plunge, many analysts believe the outlook for the “black gold” remains bleak – and in the short term it certainly is. In the long run, however, dwindling supplies, resurgent demand, and a lack of investment will cause crude oil to double, triple, or even quintuple in price over the next few years.

In fact, the Paris-based International Energy Agency (IEA) – energy advisor to 28 industrialized nations – says oil will rise to $100 a barrel by 2015, as a result of a major “supply crunch,” and will ultimately soar to $200 a barrel.

But before it does, prices are likely to sink even further, perhaps falling as low as $20 a barrel in the first quarter of the New Year.

Indeed, much of Wall Street expects oil prices to average about $50 a barrel in 2009. Some of the firms and their specific forecasts include:

• Deutsche Bank AG (DB, which says oil prices will average $47.50 for all of next year.
• Merrill Lynch & Co. Inc. (MER), which predicts that prices will average $50 even.
• Moody’s Investors Service (MCO) also says crude will average $50 a barrel in 2009, but says that average will increase to $55 a barrel for 2010.
• Goldman Sachs Group Inc. (GS) is slightly more bearish, predicting that prices will average $45 for all of next year – after falling as low as $30 in the 2009 first quarter. (It’s worth noting that Goldman – just five months ago – predicted oil prices would hit $200 a barrel in 2009).

But analysts also agree on something else: When the recessionary tide finally recedes, all of the factors that drove oil to its record high last summer will once again be exposed, and crude again will again soar to record highs.

"We may see prices drop lower – into the twenties, even – but there’s a better-than-average chance that they’ll be back over $70 a barrel by the end of next year,” says Money Morning Investment Director Keith Fitz-Gerald. “That’s where firms like Goldman and Merrill are getting all of these ‘middle-of-the road,’ $50-a-barrel estimates. And it’s why investors who buy in through the first quarter could enjoy compelling returns at the end of the year."

In the meantime, however, low oil prices are crimping investment in new capacity, a reality that will lead to much higher prices down the road.

Just ask the IEA.

IEA: Rising Demand + Lack of Investment = ‘Supply Crunch’

According to widely respected energy advisor, global oil demand will slide 0.2%, or 200,000 barrels per day (bpd), this year, falling to an average of 85.8 million bpd. But the IEA also says that oil demand will advance by an annual average of 1.6% between 2006 and 2030.

The bottom line: Regardless of any short-term pullback, daily demand will rise from the current level of 86 million barrels to 106 million barrels in 2030. In other words, daily demand in 2030 will be 23%.

To meet that demand, the agency estimates that the world needs $26.3 trillion in supply-side investments over the next 21 years. 

China, India and other developing countries, alone, will need investments of $360 billion a year through 2030, the agency said.

About 7 million bpd of additional capacity needs to be added to the market by 2015. And right now – because of marketplace changes – the financial incentives to make that happen just don’t exist.

Exploration costs have more than quadrupled since 2000, as oil producers have been forced to take on more complex projects, and the costs of both labor and materials have skyrocketed. At the same time, the steep drop in oil prices has put even more pressure on energy companies to curtail their investments rather than increase them.

Earlier this year, for instance, ConocoPhillips (COP) and Saudi Arabia Investment Co.