When fossil fuels were formed, much of Earth was covered with swamps. The swamps were filled with trees, ferns, and other large leafy plants. The trees and plants died and sank to the bottom of the swamps. There they formed a spongy material called peat. Over many hundreds of years, sand, clay, and other minerals covered the peat. It slowly turned into rock. More and more rock was formed. The rock weighed down on the peat, squeezing all the water out of it. Over millions of years, the peat turned into coal, oil, and natural gas.

Oil also formed in the oceans. The ocean was full of tiny sea creatures called diatoms. When these creatures died, they fell to the seafloor where they were slowly covered by rock. Over time, heat and pressure turned them into oil.

Several countries in the Middle East are among the world’s largest oil producers. Canada, the United States, Russia, and China are also among the largest oil-producing countries. Oil is found on land, as well as in the oceans. Canada has a number of drilling platforms in the ocean off the coast of Newfoundland.

The largest reserves of coal are found in the United States, Russia, and China. Canada is a mid-sized coal producer. British Columbia produces about one-third of Canada’s coal.

Natural gas is usually found with oil or coal. There may also be many undiscovered fossil fuel reserves in the world.