Describe the process of formation of petroleum 

Petroleum is a fossil fuel which got formed by the dead remains of the sea animals. These animals slowly got trapped under soil and clay and more deposits were formed with time. Due to depth, the temperature and pressure raised and over the years they got converted into petroleum oil. Since oil is lighter than water, it did not get mixed with water and got raised to the superficial rocks, which did not allow it to pass through them.

Petroleum is a mixture of various useful substances. Thus, it is refined to separate these useful by-products in petroleum refineries by the process of fractional distillation of petroleum.