The fugitive emission characteristics of two sheet gasket materials, an NBR/asbest's sheet and a metal-reinforced flexible graphite sheet, were investigated with four different fluids: helium, methane, propane and sulfur hexafluoride.The effect of a moderate temperature exposure (5 days at 350F) on the gasket tightness was also studied.The tests were conducted on 4-inch NPS gaskets using the room temperature tightness test (ROTT) procedure and the newly developed emission hot operating tightness test (EHOT) procedure.During the tests, gasket leak rates were measured using either the pressure decay or the pressure rise methods.To improve the precision of the leak rate calculations, a correction for deviation from the ideal gas law was developed and applied.