Why do we find abundant oil and natural gas deposits in some parts of the world, and not in others?
When the earth was young, there was only one continent, called Pangaea. Over time, Pangaea broke apart into multiple continents, and these newly-formed continental plates went their separate ways. As the plates of the earth moved, some inland seas formed, while others were destroyed. Some of these seas became sedimentary basins—prime locations for the formation of hydrocarbons.
As microscopic organisms were buried deep in the sedimentary basins, heat and pressure transformed them into oil and gas. The sediment that buried the organic material became sedimentary rock.
What traps hydrocarbons underground?
Because hydrocarbons are less dense than the surrounding rock, underground pressure causes them to rise naturally through porous and permeable rock towards the surface. This migration continues all the way to the surface, unless the hydrocarbons encounter underground trapping structures like faults, anticlines, salt domes, or stratigraphic traps.
To learn more about the formation of sedimentary basins, hydrocarbon migration, and underground trapping structures, take a look at Energy 301: Geology of Hydrocarbons.