Petroleum, or crude oil, is formed in a similar way to coal. But instead of becoming a rock, it became a liquid trapped between layers of rocks. It can be made into gas, petrol, kerosene, diesel fuel, oils and bitumen. These products are used in houses for heating and cooking and in factories as a source of heat energy. They are also used in power stations and to provide fuel for transport. However their use, especially petrol and diesel, produces large amounts of carbon dioxide emissions. It also produces other poisonous gases that may harm the environment and people’s health. Another common use for petroleum is in producing petrochemicals such as plastics.