A mixture of hydrocarbons that stay liquid or semi-solid in subsurface reservoir.
The usual composition ranges from C1 to C32 and API gravity is between 4° and 42° (Specific Gravity is 0.816 ÷ 1.0).).
It may also include minor organic and inorganic chemical substances (< 7% in weight).
The total range of oil density is often classified in narrow ranges:
See also
Natural Science / Physics / Chemistry / Chemical Substance
Petroleum Industry / Upstream / Subsurface E&P Disciplines / Petroleum Geology / Petroleum fluids