The phrase "gaseous methane" refers to methane that is in a gas form. It means methane is in a state where it doesn't have a definite shape or volume and can freely spread in the air. Full definition
It has been shown to store 180 cubic centimeters of gaseous methane per cubic centimeter of absorbent. (sciencemag.org)
In this case we're autogenously pressurized, and then use gaseous methane and oxygen for the control thrusters. (businessinsider.com)
► In a News feature in this week's Science special issue section «Gas Revolution,» Robert Service profiles Roy Periana, a scientist at the Scripps Research Institute in Jupiter, Florida, who has dedicated his career to turning gaseous methane into methanol, cheaply and efficiently. (sciencemag.org)