The present disclosure relates to pressure relief and pressure regulating valves. More particularly, the disclosure relates to a miniature in-line fuel pressure regulator having a regulator body that includes a housing member and an adjusting member, a pin axially disposed within the regulator body, the pin including an upper end having a circumferential groove, a lower end having a fluid inlet, one or more fluid discharge ports, and a fluid passageway connecting the fluid inlet to the one or more fluid discharge ports, an elastomeric O-ring conformingly positioned within the circumferential groove on the upper end of the pin so that the elastomeric O-ring contacts the raised annular valve seat when the fluid pressure regulator is closed, and a biasing member coupled to the pin and configured to maintain the elastomeric O-ring in contact with the raised annular valve seat to control an opening pressure of the fluid pressure regulator.