Anonym (18. oktober 2007). «Oil markets explained». BBC News. Besøkt 18. desember 2018. «'Sweet' crude is defined as having a sulphur content of less than 0.5%.»
doi.org
Szymon Wlazlowski , Björn Hagströmer & Monica Giulietti (2011). «Causality in crude oil prices» (på engelsk). Applied Economics (Vol. 43 Issue24). s. 3337-3347. doi:10.1080/00036841003636250. «Crudes are considered to be sweet when the sulphur content does not exceed 0.5% and sour otherwise.»
Showkat M. Hammoudeh, Bradley T. Ewing and Mark A. Thompson (2008). «Threshold Cointegration Analysis of Crude Oil Benchmarks». The Energy Journal, vol. 29, nr. 4 (på engelsk). International Association for Energy Economics. s. 79–95. «.»