NG consists of mainly of seven hydrocarbon compounds, of which methane accounts for over 90% of the total (typically, analysts consider 96% methane content to be “standard” for NG). The seven compounds, as shown in the figure below, are (in order of the length of their molecular chain):
As the molecule chain lengthens, less pressure is required to liquefy the molecule. Pentane, for example, is a liquid at ambient temperature and one atmosphere of pressure (sea level).
Because it has the shortest molecular chain of all seven compounds, methane requires the greatest amount of pressure in order to liquefy it, which results in challenges to transport and store it. It is, therefore, the lowest-valued of the seven compounds, but it is in far greater abundance.