Question

what type of environment is needed to eventually form petroleum?
ocean with small organisms
swamp
desert/dry
cold mountains
rewatch

Explanation:

Petroleum is formed from the remains of small organisms like plankton that lived in the ocean. These organisms were buried and subjected to heat and pressure over millions of years. Swamps form coal, deserts/dry and cold - mountain environments are not conducive to petroleum formation.

Answer:

ocean with small organisms