Free gas, separate from, but overlying an oil zone that occurs within the same producing formation as oil. Since gas is lighter, it occupies the upper part of the reservoir.
The removable cap that allows you to fill your vehicle's tank with fuel. The gas cap is an emission control device because it allows air to be drawn in to the tank but prevents fuel vapors from escaping into the atmosphere.
A device that seals the evaporative emissions system of your vehicle. Every vehicle receiving an emissions test must pass a gas cap pressure test to ensure that the gas cap is functioning properly. If your vehicle's gas cap must be replaced, be sure to get the correct gas cap for your make and model of vehicle.
A layer of free gas on top of the oil zone in an underground structure or reservoir.