The common feature about all fossil fuels is that they all contain the element carbon and hydrogen.Fossil fuels are those fuels that are formed as a result of geologic processes acting on the remains of organic matter produced by photosynthesis, a process that began billions of years ago.
Examples of fossil fuels are: Coal
petroleum,natural gas,oil shales,bitumens,
tar sands, and heavy oils.
These fossil fuels are hydrocarbons which are made up mainly carbon and hydrogen with other elements such as sulfur, nitrogen, oxygen, and mineral matter.
Therefore, the common feature about all fossil fuels is that they all contain the elements, carbon and hydrogen because they are hydrocarbons.