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==Classifications or grades==
Generally speaking, oil with an API gravity between 40 and 45° commands the highest prices. Above 45 degrees°, the molecular chains become shorter and less valuable to refineries.<ref>{{cite web|title=Comments on Crude Oil Gravity Adjustments|url=http://dnr.louisiana.gov/sec/execdiv/techasmt/oil_gas/crude_oil_gravity/comments_1989.htm|publisher=Louisiana Department of Natural Resources|accessdate=6 January 2014|archiveurl=http://web.archive.org/web/20070118001025/http://dnr.louisiana.gov/sec/execdiv/techasmt/oil_gas/crude_oil_gravity/comments_1989.htm|archivedate=18 January 2007}}</ref>
[[Crude oil]] is classified as light, medium, or heavy, according to its measured API gravity.
* [[Light crude oil]] is defined as havinghas an API gravity higher than 31.1 °API (i.e., less than 870 kg/m<sup>3</sup>)
* Medium oil is defined as havinghas an API gravity between 22.3 °API and 31.1 °API (i.e., 870 to 920 kg/m<sup>3</sup>)
* [[Heavy crude oil]] is defined as havinghas an API gravity below 22.3 °API (i.e., 920 to 1000 kg/m<sup>3</sup>)
* Extra heavy oil ishas defined withan API gravity below 10.0 °API (i.e., greater than 1000 kg/m<sup>3</sup>)
NotHowever, not all parties use the same grading.<ref>Crude oil grades, Crudemonitor.ca, web PDF file: [http://www.crudemonitor.ca/quickfacts/misc/grades.pdf CMonitor-Gr-PDF]</ref> The [[United States Geological Survey]] uses slightly different definitionsranges.<ref>USGS FS2006-3133_508, web PDF file: [http://pubs.usgs.gov/fs/2006/3133/pdf/FS2006-3133_508.pdf USGS-508-PDF]</ref>
Crude oil with API gravity less than 10 °API is referred to as [[extra heavy oil]] or [[bitumen]]. Bitumen derived from the [[oil sands]] deposits in the Alberta, Canada area, has an API gravity of around 8 °API. It can be diluted with lighter hydrocarbons to produce [[diluted bitumen]], havingwhich has an API gravity of lowerless than 22.3 API°, or further "upgraded" to an API gravity of 31 °API to 33 °API as [[synthetic crude]].<ref>Canadian Centre for Energy Information. [http://www.centreforenergy.com/AboutEnergy/ONG/Oil/Overview.asp?page=2 "What is crude oil?"]. Retrieved on: 2012-09-10.</ref>
==See also==
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