Organic compounds are generally any chemical compounds that contain both carbon and hydrogen, and they are the basis of all known life. The simplest organic compound is methane, which contains only these two elements, but most organic compounds also contain additional elements, usually oxygen, nitrogen, sulfur and/or phosphorous.
Organic compounds differ from each other because of differences in the numbers of atoms of each element in their molecules and in the types of bondings between the individual atoms. The total number of organic compounds is vast, with estimates for currently known ones, both natural and synthetic, ranging from more than ten million to as many as twenty million. This is far greater than the number of inorganic compounds, and it is a result of the unique structure of carbon and thus its unique bonding capabilities.
The most abundant organic compound is cellulose, which is the main constituent of plant fiber. Most synthetically produced organic compounds are derived from petrochemicals, which were formed through the degradation of organic matter underground at high pressures and temperatures over millions of years.