Petroleum & Natural Gas
Petroleum and natural gas are the signature fuels of the modern world. Their discovery in the 19th century and then rapid development in the 20th century fueled unprecedented economic expansion. Petroleum is especially important as a liquid fuel for the world's transportation system and as a petrochemical feedstock from which plastics and chemicals are made. Swings in the price of petroleum affect the entire economy. Natural gas is valued as relatively clean burning fuel for electricity generation and space and water heating. Both fuels release significant quantities of carbon dioxide when burned, and thus contribute to global climate change.