The report I read is that it takes 2 boe of gas to produce 3 boe of oil from the tar sands. Because they are running out of the stranded gas, and because Canada is in violation of their Kyoto agreement, there is serious talk of building nukes to provide the heat and electric power to extract oil.
It seems like a lot of people are in violation of their Kyoto treaties, UK included. Perhaps sustainable/ecologically conscious growth will prove to be the oxymoron many have long professed it to be.