The oil industry takes great care to protect the environment. However, occasionally an oil tanker accidentally spills oil into the sea. If it isn't cleared up, the spilt oil can damage sea birds and other animals. It can also make a mess on rocks and beaches. If oil is spilt, the oil company tries to stop it from spreading and will remove it when this is practical.
Oil and other fossil fuels produce carbon dioxide when we burn them. Too much carbon dioxide can trap heat in the Earth's atmosphere, leading to global warming. That's why we are trying to cut back on burning these fuels.