Black gold mine

To its champions it represents a plentiful, secure source of fuel that could wean the West off its addiction to Middle East oil. To its detractors it is an environmental catastrophe in the making.

Despite the strong feelings on both sides, most agree that the oil-sand beneath the soil of Alberta, Canada represents the largest petroleum resource on the planet.

Canada’s oil-sand reserve covers an area about twice the size of Wales and already hosts most of the world’s oil majors plus a smattering of home-grown specialists. Between them they produce about 1.3 million barrels of crude oil a day from this unpleasant mixture of clay, sand, water and bitumen.

But there is much, much more — an estimated 1.7 trillion barrels more, or two thirds of the world’s remaining petroleum reserves. Despite a recent slowdown triggered by the falling price of crude, there are plans to scale up production to 3.5 million barrels a day over the next decade.