How do oil sands affect emissions?

Greenhouse emissions of tar sand, per barrel, are more than conventional crude oil. This is because, it takes more energy to extract the bitumen from the tar sand and more so, to convert the bitumen to usable oil taking up even more energy. This energy is usually derived from burning natural gas. Emissions by tar sand are approximately 100 kg CO2 per barrel while conventional oil is approximately 30 kg CO2 per barrel.