Shell began drilling test wells this month that will inject carbon dioxide from its Scotford upgrader plant deep into a porous rock formation where it will be trapped.

Officials say the project could trap about 40 percent of the Alberta plant's emissions by 2014.

The Seattle Times reported Sunday that carbon dioxide is a significant drawback to the development of oil sands. The processing of the oil-soaked dirt in plants such as Scotford spews large amounts of greenhouse gas into the atmosphere.

Environmentalists say greenhouse gases make oil sand an undesirable energy option; however, the Times said James Smith, Shell's country chairman for the United Kingdom, said after a recent tour of the oil sands: "We want something that's clean and cheap and always on. None of our current sources of energy fits the bill."