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crude.”Crude oil that does not contain hydrogen sulfide is classified as
“sweet crude.”
REFINED HYDROCARBONS
Oil refineries put crude oil through several chemical and
physical processes to render it into many useful products such as
gasoline, kerosene, and diesel fuel. These refined products are
mixtures, or blends, of several hydrocarbons that liquid under normal
conditions. Generally, gasoline is made up of liquid hydrocarbons that
are lighter in weight (less dense) than the liquid hydrocarbons that
make up and diesel fuel.
OIL AND GAS RESERVOIRS

Hydrocarbons and their associated impurities occur in rock
formations that are usually buried thousands of feet or metres below
the surface. Scientists and engineers often call rock formations that
hold hydrocarbons “reservoirs.”
Oil does not flow in underground rivers or pool up in
subterranean lakes, contrary to what some people think. And, as
you’ve learned, gasoline and other refined hydrocarbons do not
naturally occur in pockets under the ground, just waiting to be drilled
for. Instead, crude oil and natural gas occur in buried rocks and, once
produced from a well, companies have to refine the crude oil and
process the natural gas into useful products. Further, not every rock
can hold hydrocarbons. To serve as an oil and gas reservoir, rocks
have to meet several criteria.

Characteristics of Reservoir Rocks
Nothing looks more solid than a rock. Yet, choose the right
rock – say, a piece of sandstone or limestone – and look at it under a
microscope. You see many tiny openings or voids. Geologists call
these tiny openings “pores”. A rock with pores is “porous” and a

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