Bitumen is a solid. Surface deposits make up about 20% of tar sand reserves. To extract bitumen, huge excavators scrape away the topsoil and the underlying tar sands are lifted into huge dump trucks. Tar sand or bitumen is a solid with has to be diluted to a liquid for transport. Natural gas condensate and chemicals used to dilute tar sand are called diluents, hence the name "diluted bitumen" is often used to describe tar sand crude.
The superficial tar sands are then trucked to extraction processes, where they are steamed to extract the heavy, bitumenous oil.
This first step of tar sand extraction is estimated to result in gasoline that carries a burden of "at least five times more carbon dioxide" than product realized from conventional "sweet crude" oil production.
Because the remaining 80 percent of the sands are too deep to be mined, steam is injected into these deeper oil sands, loosening the bitumen and allowing producers to draw it upward .
Before tar sand is refined and turned into heavy crude, it has to be diluted to flow through a pipeline.
Since bitumen has the composition of asphalt and tar, it is liquified with diluents and then highly pressurized (up to 1600 psi) causing high heat (158º) due to friction.
The diluents include natural gas condensate and other hazardous chemicals including hydrogen sulfide, benzene, and toluene.
These diluents greatly increase the toxicity of tar sand which already contains some naturally occurring heavy metals when mined.
Diluted bitumen or “Dilbit” tar sand oil is a highly corrosive, acidic, and potential unstable blend of thick raw bitumen and volatile natural gas liquid condensate.
Unlike some tar sands crude which has been upgraded before transported such as Syncrude, this material is carried in its corrosive raw form.
Bitumen blends contain up to twenty times higher acid concentrations than conventionnal crude, and up to ten times as much sulfur. Dilbit is also up to seventy times more viscous than conventional crude oil.
3.^ Fossil Fuels IV, Daniel Holland, Illinois State University, Physics professor, http://www.phy.ilstu.edu/~holland/phy207/Fossil_Fuels_4.ppt
4.^Gareth Crandall, Non-Conventional Oil Market Outlook, Presentation to: International Energy Agency, Conference on Non-Conventional Oil, 2002, p. 4, http://www.docstoc.com/docs/1029829/Non-conventional-Oil-Market-Outlook or http://www.iea.org/wor/2002/calgary/Crandall.pdf
5.^Canadian Crude Quick Reference Guide Version 0.54, Crude Oil Quality Association, 2009, http://ww.coqa-inc.org/102209CanadianCrudeReferenceGuide.pdf