To meet the objective of reducing greenhouse gas emissions, whole life cycle emissions need to be accounted for. (eco-business.com)
Now, extraction technology may improve, but those un-economic barrels will be hard to get, so let's assume that today's life cycle emissions per bbl remain constant over time. (andrewleach.ca)
A literature review of numerous energy sources CO2 emissions by the IPCC in 2011, found that, the CO2 emission value that fell within the 50th percentile of all total life cycle emissions studies conducted was as follows. (en.wikipedia.org)