Petroleum contains hydrocarbons. After distillation, it still contains chemical compounds with sulfur, oxygen and Nitrogen as well as other unwanted compounds, such as Alkalenes. Processed petroleum is used for lubricants; the substances mentione are unwanted in lubricants as they can speed up the aging process. For this reason, they are extracted using a process called hydrogenation. In hydrogenation, Hydrogen sulfide and ammonia gases are produced. These gases require special handling, as they are very toxic.