Whether or not conventional oil has a "peak," the world’s heavy oil reserves have only just been tapped. In fact, some experts estimate that heavy oil represents more than half of the globe’s known reserves - and those are just the known resources. Many heavy oil deposits remain unexplored.

A great number of heavy oil wells rely on horizontal completions and are thus prone to the flow control challenges inherent to this type of completion such as the "heel-to-toe" effect from friction loss along the wellbore, as well as pressure, fluid mobility and permeability contrasts in the producing section. There is a natural tendency to have much higher production at the heel (near the vertical part of well) than the toe (at the end of the well).

When analysts try to estimate the world’s remaining oil reserves, one of the largest variables is heavy oil. The question is not how much is in the ground, but how much of it can be recovered. For Canada’s heavy oil operators - those who could make Canada the world’s fifth-largest producer by 2015 - the answer depends on the efficiency of their recovery plans. If heavy oil is in your portfolio, here are some points to consider.

China has one of the world's most voracious appetites for oil. Its rapidly growing demand is so strong, in fact, that it has pushed the country to develop all the limited oil resources it has available--even heavy oil reserves in hard-to-reach locations.

Soon, the world’s fourth-largest island may be known more for heavy oil than it is known for the ring-tailed lemur. Experts estimate that half of the island is covered by the heavy oil-rich sedimentary basins of Morondava, Majunga and Ambilobe.

Long regarded as virtual pariahs among crude oil feedstocks, heavier slates of crude are increasingly proving their worth at oil processing facilities worldwide. Cheaper to buy but costlier to refine, heavy oils have often taken the proverbial back seat to more expensive but easier-to-process light- and medium-gravity crudes. Now, heavier crudes are getting their due.

Getty's formula has worked for American oil enthusiasts, yet oil is becoming increasingly difficult to find -- let alone recover. Among other concerns, peak oil theories and geopolitical agitations in OPEC nations have left operators scrambling to find inexpensive, more efficient methods of recovering nonconventional hydrocarbons, like heavy oil, that will satisfy the world’s demand for petroleum into the next century.

Heavy oils are found around the world, with an estimated 69 percent of the world's technically recoverable heavy oil and 82 percent of the technically recoverable natural bitumen located in the Western Hemisphere.

Success with heavy oil depends as much on understanding the fluid properties of the reservoir as it does on knowing the geology of the reservoir itself. The reason is that the chemical differences between heavy oil and conventional oil ultimately affect their viscosity.

Because the challenging, yet almost entirely untapped, deposits of heavy oil hold some of the largest reserves of hydrocarbons in the world. According to Bill Bush of the API, "Heavy oils, oil sands, and potentially shale, could contribute substantially to future U.S. and world oil supplies."

Used in previous centuries for various tasks, the bitumen found in Alberta's Athabasca Oil Sands may serve another purpose: securing Canada's role as an important oil producer with nearly 500 billion barrels of potential oil.

Husky Energy, a fixture in Canada’s oil and gas industry for 60 yrs with extensive experience in heavy oil production, recently completed construction of its first-ever oil sands project.

Brazil is set to achieve energy self-sufficiency this year, thanks in large part to its production of heavy oil. Most of its crude oil production is offshore in the Campos, Espírito Santo, and Santos basins in deep and ultra-deep waters.

For decades, Russia has been a major player on the global energy scene. At times, the vast country has even bested Saudi Arabia as the world's top oil producer. Throughout history, the country has relied on its largely mature supply of conventional oil.

Home to the world's largest single accumulation of heavy and extra-heavy oil, Venezuela boasts an estimated 1.2 trillion barrels of oil in place. Approximately 270 billion of those barrels could be recovered and produced from the Orinoco Heavy Oil Belt.

Because heavy oil is so viscous, conventional methods, such as vertical wells, pumps, and pressure maintenance, are inefficient at extracting the oil. So, new technologies are being used to recover heavy oil including: cold heavy oil production with sand (CHOPS), vapor extraction (VAPEX), and thermal in situ methods.

Until recently, many producers thought commercial quantities of heavy oil were unique to a handful of large fields in Canada, Venezuela and the United States. Now that market conditions have changed, prospects are quickly opening up around the world.

Heavy oil is thick crude oil that is viscous and has a low API gravity, making it difficult to produce using conventional methods.