Re: Is it true that oil that comes right out of the ground is very hot, and why

In my early career as a geologist, I worked on oil rigs. I observed that any
fluids coming out of the ground were hot, and that the heat increased with 
depth, at approximately 1 degree Celsius per 100 feet of depth. The hottest
fluids I observed (water, mud and oil) arrived at the surface at approximately
130 degrees Fahrenheit, and that was after cooling a bit on the way up.
So, yes, oil is hot (relative to the earth's surface) when it comes up.

Why?
It is accepted by earth scientists that heat in the earth comes from two
sources: 1) the original accretion of the earth, and 2) due to radioactive decay.
1) During the formation of the earth, the planet was continually bombarded by
solar system debris, asteroids, dust, planetisimals and meteors. At each 
impact some of the kinetic energy was transformed into heat.

2) Radioactive minerals change over time (decay) and the decay process results
in a change in the mineral, some release of gas (occasionally) and some heat.
Heavier elements (including radioactive elements) eventually migrated inward to
form the core. This core became the hottest part of the earth.
The heat from the earth's core continuously flows outward. It transfers
(conducts) to the surrounding layer of rock, the mantle. When temperatures and 
pressures become high enough, some mantle rock melts, becoming magma. Then,
because it is lighter (less dense) than the surrounding rock, the magma rises 
(convects), moving slowly up toward the earth's crust, carrying the heat from
below. 

Sometimes the hot magma reaches all the way to the surface, where we know it as
lava. But most often the magma remains below earth's crust, heating nearby rock 
and water (rainwater that has seeped deep into the earth) - sometimes as hot as
700 degrees F. Some of this hot geothermal water travels back up through faults
and cracks and reaches the earth's surface as hot springs or geysers, but most
of it stays deep underground, trapped in cracks and porous rock. This natural
collection of hot water is called a geothermal reservoir.

Oil also is heated, and that's why oil is hot.  I hope this helps. You might
want to also look at the following websites.

Best regards,

Mike Munsil, P.G.
 http://geothermal.marin.org/GEOpresentation/sld005.htm

 http://www.newton.dep.anl.gov/askasci/env99/env162.htm

 http://dev.nsta.org/ssc/moreinfo.asp?id=966