Petroleum

The word petroleum is derived from the Latin word Petra, meaning rock and oleum meaning oil. Petroleum is derived rocks where it flows freely either in liquid or gaseous state. It has been used for thousands of years by ancient civilizations for all sorts of purposes.
Petroleum is an inflammable mixture of oily hydrocarbons with very complex chemical properties. The best petroleum grade is that which has a high carbon content and a low hydrogen content. The three grades of petroleum are paraffin-base oil, asphalt-base oil and mixed base oil.
Paraffin base oil contains a high percentage the lighter hydrocarbons such as methane and yields the commercially more valued products such as paraffin and high grade lubricating oil.
Oil believed to have been formed from the dead organic matter and other decomposed materials which were deposited on the sea bed. When sedimentary rocks accumulated on the seabed, it compacted and pressure forced the decomposed matter to turn into oil. It occurs in places where there are marine sedimentary rocks in the ocean depths such as mud stone, shale, sandstone or limestone. It is trapped in the pore spaces of sedimentary rock.