Question

how petroleum formed?

Answer 1

petroleum was formed millions years ago due to natural calamity the anymals and plants were traped inside the soil
so many year's latter the petroleum was formed

Answer 2

$\textbf{Formation of Petroleum }$:

When remains of the dead organisms sank to the bottom of the sea, they get converted by sand and clay.

After millions of years under the combined effect of high temperature, high pressure and bacteria in the absence of air, petroleum forms.

The petroleum so formed passes through porous rocks untill it got trapped between some impervious rocks.