A mixture of low density hydrocarbons that stay liquid in subsurface reservoir.
The usual composition ranges between C4 and C8 and API gravity is in the range of 31.1° ÷ 42° (Specific Gravity = 0.816 ÷ 0.87).
It may also include minor organic and inorganic chemical substances (usually < 7% in weight).
See also
Natural Science / Physics / Chemistry / Chemical Substance