Geophysical Service Inc. (often abbreviated GSI) was a Texas-based company founded by John Clarence Karcher and Eugene McDermott in 1930,[1] for the purpose of using refraction and reflection seismology to explore for petroleum deposits.

On December 6, 1941, the company was purchased by Eugene McDermott, Cecil Howard Green, J. Erik Jonsson, and H.B.

On July 3, 1981, MS Arctic Explorer, chartered to GSI to conduct seismic surveys off the Labrador coast for British Petroleum, sank off St. Anthony, Newfoundland, in the Strait of Belle Isle, resulting in the loss of 13 lives.

GSI is the largest owner of marine seismic data in Canada, with its head office located in Calgary, Alberta.

In 2013, GSI was involved in several cases of litigation for damages over disclosure of its confidential seismic data.