Couch Oil And Gas. Hydrocarbons have multiple structures and functions. They are used as an energy resource, and most frequently as a source of fuel. Because of their multi-dimensional nature, hydrocarbons can be classified into four distinct groups: saturated, unsaturated, aromatic, and cycloalkane. They can take the form of a gas, liquid, solid, or polymer, and depending on the classification and form, can be used for distinct functions. Hydrocarbons are important as a main energy resource, and are currently used for the bulk of our electrical energy.