The easy oil is gone so where do we look now?

The Canadian oil sands should of course also be included in the matrix of future oil supply. Despite the difficulty and higher-cost, compared to conventional sources, of stripping the bitumen from the oil sands and processing it into heavy oil, the vastness of the reserves contained in the sands of northern Alberta cannot be underestimated. According to the Alberta government the oil sands has proven reserves of about 168 billion barrels, the third largest proven crude oil reserve in the world, after Saudi Arabia and Venezuela. Canadian oil sands production is forecasted to grow from about 2 million barrels per day to 3.7 million barrels per day by 2020 and 5.2 million barrels per day by 2030, according to Alberta Energy.

Many have pointed to the Arctic as the answer to the depletion of existing oil and gas fields. The region, which crosses Russia, Alaska, Norway and Greenland, is estimated to hold 166 billion barrels of oil equivalent, more oil and gas than Iran and enough to meet the world's entire consumption of crude oil for five years, reported The Daily Telegraph.

Drilling down a bit further, the US Geological Survey estimates that over 87% of the Arctic's oil and gas resources are located in seven Arctic basin provinces: Arctic Alaska Basin, East Barents Basin, East Greenland Basin, West Greenland East Canada Basin, East Greenland Rift Basin, West Siberian Basin and the Yenisey-Khatang Basin.

The Prudhoe Bay field in Alaska, which has been pumping oil since 1977, is the largest oil field in North America, at about 25 billion barrels. Around 16 percent of the Arctic's undiscovered oil and gas is located on land, with the remaining potential either locked in continental shelves or underwater at depths over 500 meters.

Of the seven basins outlined by the USGS, the most abundant is Arctic Alaska, at 29.36 billion barrels of crude oil, followed by the Amerasia Basin, at 9.72 billon, and the East Greenland Rift Basin at 8.90 billion, according to Geology.com.

Among the oil majors eyeing the Arctic prize, Shell has been drilling off the coast of Alaska for decades, Statoil is active in the Norwegian Arctic, and ExxonMobil is exploring with Russia's Rosneft in the Russian far north. Last year Rosneft/ ExxonMobil discovered a field that could hold up to 730 million barrels of oil, but for the time being, exploration looks thin. With low oil prices, most oil companies are reining in capital costs, and exploration expenditures are a high-priority line item. Statoil and Chevron have both put their Arctic plans on ice, and the ExxonMobil partnership with Rosneft could be in trouble due to Western sanctions against Russia. Shell is currently the only company sinking any capital into the Arctic, with the Anglo-Dutch firm announcing at the end of January that it plans to proceed with a $1-billion Arctic drilling this summer.

And what of the shale oil reserves that have propelled the United States to becoming close to energy-independent and threaten to knock Saudi Arabia off its pedestal as the world's top oil producer? In 2013, the EIA conducted the first-ever U.S. analysis of global shale oil reserves. It estimated "technically recoverable" (as opposed to economically recoverable) shale oil resources of 345 billion barrels in 42 countries, the equivalent of 10 percent of global crude oil supplies – and enough to cover over a decade of oil consumption.

According to the EIA, Russia and the United States have the largest shale oil resources, at a respective 75 billion barrels and 58 billion barrels, followed by China, Argentina and Libya. The other countries on the top 10 list of countries with technically recoverable shale include Australia, Venezuela, Mexico, Pakistan and Canada.

The EIA report also shows a marked increase in the number of prospective shale deposits globally compared to an earlier 2011 report. That report listed 32 countries with shale versus 41 in 2013, 48 basins versus 95, and half the number of formations, at 69 in 2011 versus 137 in 2013.