A high-pressure fuel system supplies gaseous fuel to an internal combustion engine. Gaseous fuel pressure within the system is at least 17 MPa during normal operation. The system comprises a number of components and conduits and at least one resilient member for sealing at an interface between two components. The resilient member consists essentially of thermoplastic polyurethane. A corresponding method provides sealing between components containing gaseous fluids at pressures that can be above 17 MPa, in which the gaseous fluids routinely undergo rapid reductions in pressure. The method comprises disposing a resilient member, which consists essentially of thermoplastic polyurethane, at an interface between the components. Gas pressure fluctuations can occur during operation of the components or when the high-pressure gas is vented from the components upon shut down of the high-pressure system. A particularly suitable application for the present method is high-pressure gaseous fuel supply systems for internal combustion engines.