Canada is now one of the world's energy superpowers.

Over the past two decades, changes in technology and the rising cost of oil have left it with so much recoverable oil in the sands, rocks and clay of the province of Alberta that it is now believed to hold the third largest reserves on earth - after Saudi Arabia and Venezuela.

But most of that is so far un-tapped, with Canada accounting for little over 4% of global oil production in 2010 according to BP's annual statistical review.

To increase that share it must gain global acceptance of the heavy, sticky and, some say, more polluting oil it has found.

For Canada's government, the world has no choice - despite its climatic consequences.

"You can turn off your lights and freeze in the dark, the alternative is to use the energy, which of course you are using, everybody is using," says Joe Oliver, Canada's minister for natural resources.

Export problems

Image caption Rocks containing bitumen are broken up using water and chemicals to extract the oil

But for ministers meeting at the latest climate change summit in Durban, South Africa, the decision on whether to embrace new, more polluting, forms of fossil fuel may seem less obvious.

In both the US and EU there is mounting opposition to importing oil mined from tar sands.

In the US, President Barack Obama has delayed a decision on a major new pipeline between Canada and the US until after the next election.

And in the EU, the European Commission is pushing legislation which would see Canadian oil classified as more damaging to the environment than some other oil imports, effectively limiting future demand.

Canadian oil seems a far less popular product than the country's staple sticky export, maple syrup.

'Tar sands'

The latest BP review estimated that, in 2010, Canada had more than 175bn barrels of recoverable oil - just behind Venezuela at 211bn and Saudi Arabia's 264bn.

Where is the oil? Source: BP statistical bulletin for 2010

But not all oil comes out the same.

Whilst Saudi oil is relatively light and comes out of the ground relatively easily - at a cost often of less than $10 a barrel - Canadian oil is heavy, sticky and can cost more than $60 a barrel to extract.

Most of Venezuela's oil fits into the same category - though it is extracted differently.

This high cost makes extracting Canadian oil more risky; investment almost ground to halt during the recession as the price of oil fell below the cost of production.

The product produced is called bitumen - often labelled as tar by its opponents.

"First of all, they are not tar sands, they're oil sands," says Mr Oliver.

To be extracted, the oil - or tar - must first be separated from a mix of sand and clay, a process which is both energy and water intensive.

Some environmentalists, and the EU, argue that this means that burning oil extracted from oil sands emits more carbon dioxide than burning oil from more conventional sources.

EU battle

In proposed EU legislation, oil from oil sands is given a greenhouse gas value of 107 grams of carbon per megajoule of energy produced, compared with conventional crude's allocation of 87.5 grams.

That is to say, if you burn oil from oil sands in your car - rather than from reservoirs under the Saudi desert - you will, overall, have been responsible for about 19% more Co2 emissions.

Image caption Oil sands extraction is energy intensive

If agreed, the EU says, the rules would complete legislation introduced in 2008 to reduce the carbon intensity of EU transport fuels by 6% by 2020.

For Canada, which already must cope with a relatively high cost of production, it would make it almost impossible to export to the economic bloc.

"It would virtually create a ban against tar sands in the EU," says Greenpeace's Charlie Kronick.

Currently, oil from sands accounts for just 0.01% of EU fuels but as more comes on stream this could increase significantly.

If the world doesn't want our oil, it doesn't have to buy our oil Joe Oliver, Canadian Minister for Natural Resources

"Of course we know that this percentage will only increase over the coming years," says EU spokesperson Isaac Valero Ladron

Last week, Canada's national energy board said it expected production from oil sands to triple by 2035 to 5.1m barrels a day.

"I think it's very clear the signal that we are sending here in Europe about tar sands," adds Mr Ladron.

But which way Europe goes will ultimately be decided by its member states - through a qualified majority vote.

So far, the UK is reported to oppose the change, backed by some Eastern European states which hope to have their own reserves of un-conventional oil to export.

"It's absolutely balanced on a knife edge," says Mr Kronick.

The vote is likely to be influenced by events in the US - which is, in the short term, where Canadian tar sands would probably go to be exported to the EU.

US worries

Their approval had been expected for a new pipeline from Alberta and through the US to Texas earlier this year, the Keystone XL.

The new route - which follows from the existing Keystone pipeline - would not only help transport the oil to the US, but would give greater access to Texan-based refineries and ports able to export to fast growing Asian markets.

Indeed, Chinese firms are increasingly taking an active role in the oil sands industry, taking stakes in Canadian firms.

Image caption Demonstrators took their case to the US capital, Washington DC

On Monday, one of China's three main state-owned oil and gas producers, CNOOC, said it had completed its takeover of troubled oil sands producer OPTI Canada, the latest in a string of investments.

However, the $7bn (£4.4bn) pipeline, which could have increased exports to the Far East, has now been delayed.

The US state department - backed by Mr Obama - has asked for the company to consider alternative routings after complaints by environmentalists and legislation in the state of Nebraska which may have blocked the planned route.

The delay will last until after the presidential election, saving Mr Obama from a tricky pre-election decision.

Carbon cost

Ultimately, the fate of oil from Alberta's sands is intricately linked to the climate change negotiations on the other side of the planet.

If leaders eventually agree on a global cost for carbon dioxide emissions it could make extracting oil from sand simply uneconomic.

Image caption Piping the oil out of Canada could increase the world's oil supply

Instead, investment may go into alternative forms of energy and investors in oil sands may lose out.

But until then, for Canada, it is simply a question of supply and demand.

"If the world doesn't want our oil, it doesn't have to buy our oil," says Mr Oliver.

Much of the world may want to buy it - but Canada is having trouble getting it to them.