The viscosity of a fluid can be expressed as a "dynamic viscosity" and a "kinematic viscosity". Be careful when comparing figures to verify comparison of like types. Dynamic viscosity is measured in units called "centipoise". Kinematic viscosity takes into account the fluid density and is measured in units called "centistokes". It is also important when comparing values to note the temperature the measurements were taken at. In general the viscosity of a liquid will be reduced as the temperature rises. For example, the range of viscosity seen for Rapeseed Methyl-Ester in the chart is 4.43 to 6.7 centistokes at 40°C; this drops to around 2.4 centistokes at 100°C.

The following chart shows the kinematic viscosity for various diesel and biodiesel fuel standards, along with a sample of reported measurements for various types of biodiesel (methyl or ethyl esters). (Note that before transesterification the vegetable oil input to biodiesel production has kinematic viscosities somewhere in the 30-50 centistoke range at 40°C which would display off the right side of the chart. Automobiles that run on "straight vegetable oil" aka SVO pre-heat the oil to bring the vegetable oil viscosity down to below 10 centistokes. For example the viscosity of corn oil at 100°C is around 8.6 centistokes. Rapeseed oil has a viscosity of 34 centistokes at 40°C. When heated to 100°C [212°F] this drops to 7.8 centistokes.)

Sources for viscosity numbers:
http://journeytoforever.org/biodiesel_yield2.html#fuelfats
http://www.biofuels.fsnet.co.uk/comparison.htm
http://www.nrel.gov/docs/fy03osti/31460.pdf
http://www.rampump.com/handbook/common2.html
http://www.oilpress.com/data-rape.htm
http://www.biodiesel.org/resources/reportsdatabase/reports/gen/20000501_gen-308.pdf