Crude oil, or its substitutes, will be produced for decades, but at an increasingly expensive tariff, both in terms of cost and energy, as it is sourced in the form of a heavy, sour (high-sulphur) material, or in synthetic form from tar-sands, shale and coal.

FORBES: Dr Richard Pike (1950-2011) and Peak Oil

Over the past year or so, opposition to new tar-sands projects has been steadily growing.

NEWYORKER: Unconventional Crude

Both Mr Obama and Mr Harper made particular mention of carbon capture and sequestration, an unproven and expensive technology that could eventually be used on the coal plants that produce about 70% of American electricity, or on the upgraders and refineries in the tar sands.

ECONOMIST: Stephen Harper looks to Washington, not Alberta

"Canadians must give up their tar sands and go back to making beer or whatever, " he said.

FORBES: Obama Down, Stocks Up (And Vice Versa)

Furthermore some potential substitutes for, or new sources of, oil (such as biofuels and tar sands) are a lot less efficient, in the sense that they require significant amounts of energy simply to produce.

ECONOMIST: The economic impact of high oil prices

It is estimated that by 2012 tar-sands operations will consume two billion cubic feet of natural gas a day, or enough to heat all the homes in Canada.

NEWYORKER: Unconventional Crude