The formation of Oil is from the remains of animals and plants that lived millions of years ago in a marine (water) environment.  Over the years, the remains were covered by layers of mud.  Heat and pressure from these layers helped the remains turn into what we today call Crude Oil .  The word "Petroleum" means "rock oil" or "oil from the earth."

The term petroleum is normally used as a common denotation for crude oil (mineral oil) and Natural Gas, i.e., the Hydrocarbons from which various oil and gas products are made. Petroleum, then, is a collective term for hydrocarbons, whether solid, liquid or gaseous.

According to the basic definition, an oil is an organic compound that is insoluble or not readily soluble in water. It could be a petroleum-based product as Well as a non-petroleum product — both categories comprise a number of different kinds of oils.

"Oil" or "oils" are concepts that do not necessarily refer to petroleum. Oil products used for energy or transportation or as raw material for plastics are mineral oils petroleum-based oils) produced from crude oil

In the Ocean 300 to 400 million years ago. Tiny sea plants and animals died and were buried on the ocean floor. Over time, they were covered by layers of sand and silt. Over millions of years, the remains were buried deeper and deeper. The enormous heat and pressure turned them into oil and gas.

As this organic mix was forced farther downward and was subjected to pressure from the rocks above and heat from the inner earth, it cooked for a few million years or so. This unsavory stew of former life eventually became fluid.

Because oil is a relatively light liquid, it will migrate above denser fluids, such as water, unless confined in what geologists call a hydrocarbon trap. A hydrocarbon trap consists of porous rock that acts as sort of an oil-holding sponge and a roof of non-permeable rock to prevent oil from moving upward.

Today, we drill down through layers of sand, silt, and rock to reach the rock formations that contain oil and gas deposits.