A natural gas detection system is provided for use with a vehicle. A natural gas detector apparatus is mounted to the vehicle so that the vehicle transports the detector apparatus over an are of interest at speeds of up to 20 miles per hour. The detector apparatus includes a transmitter section and a receiver section displaced a preselected distance from each other. The transmitter section has a light source transmitting a light beam to the receiver section forming a beam path therebetween. The apparatus is arranged such that natural gas intercepts the beam path and absorbs representative wavelengths of the light beam. The receiver section receives a portion of the light beam onto an electro-optical etalon for detecting the gas. A method of detecting natural gas is also provided. The method has the steps of providing a vehicle and mounting a natural gas detector apparatus to the vehicle. The detector apparatus has a transmitter section and a receiver section displaced a preselected distance from each other. The transmitter section includes a light source. The method includes transmitting a light beam in a beam path from the transmitter section to the receiver section, and driving the vehicle over an area of interest so that natural gas intercepts the beam path and absorbs representative wavelengths of the light beam. Fhe method also includes receiving a portion of the light beam in the receiver section so that the light beam is directed into an etalon, and detecting a gas leak in the area of interest from the portion light beam using the gas detection apparatus mounted on the vehicle while the vehicle is in motion.