Abstract: We have found it possible to investigate subsurface formations in the expectation of locating promising gas fields by a unique refraction seismic technique. Basically one carries out a two-way seismic refraction profile for a fixed spread of geophones and explosions (or equivalent impulse sources) beyond the critical reflection range for shallow refractors, but still rather close to the spread. Then without moving the spread, reproducible records are also made for a two-way seismic refraction profile with the explosions or equivalent sources spaced as far away as convenient, so the refraction paths to the detector groups in the spread is up-going to the detectors for the maximum thickness of beds intervening between the refractor and the group of geophones.