Abstract: A hydrostatic tester that may be sequentially disposed in stands of tubular members as they are lowered into an oil well bore in which gas under substantial pressure may develop. During the period when the hydrostatic tester is disposed in a stand of tubular members but not in use, an improvement operatively associated with the hydrostatic tester automatically vents gas from the bore hole to the ambient atmosphere prior to the gas pressure building up in the bore hole to the extent that the hydrostatic tester will be blown from the tubular stand with possible injury to the testing crew.