Crude oils are generally classified according to their physical properties. It can be classified based on its color, refractive index, odor, density, boiling point freezing point, flash point, and viscosity. Density (specific gravity) and viscosity are the most important physical properties to classify crude oil. The specific gravity of liquids is defined as the ratio of the density of the liquid to the density of the density of water, both at specified conditions of pressure and temperature.
For most of the crude oil value of specific gravity generally ranges from about 0.75 to 1.00.
API GRAVITY: Expressed mathematically as
ץ ═ 141.5
131.5 + ÅPI
Or ÅPI = ———— ---- 131.5
Where is the specific gravity and the is ץÅPI is the API gravity.
Other physical properties of liquid petroleum are frequently correlated with API gravity and viscosity.