The term 'petroleum source' can be summarized as a type of sedimentary rock that contains hydrocarbons, which are used to produce oil and gas. One example of a petroleum source is shale, which is a fine-grained sedimentary rock composed of mud and clay particles. Shale is formed from the compaction of silt and clay-size mineral particles, and it is often found in layers beneath the surface of the earth. Shale is an important source of oil and gas, and it is often used in the production of petroleum products.