A mixture of high density hydrocarbons that stay liquid in subsurface reservoir.
The usual composition ranges between C8 and C16 and API gravity is in the range of 10° ÷ 20.7° (Specific Gravity = 0.93 ÷ 1.0).
It may also include minor organic and inorganic chemical substances (< 7% in weight).
See also
Natural Science / Physics / Chemistry / Chemical Substance