Abstract: An effective and efficient orifice plate is provided to accurately and safely measure the flow rate of gases and liquids. Advantageously, the orifice plate prevents leakage, spillage, and dripping of hot hydrocarbon liquids and gases and other fluids. To this end, the orifice plate comprises an annular disk with special front and back surfaces. The special front and back surfaces have a flat fluid-engaging barrier portion which contact the fluid stream about the flow passageway and have a grooved portion which extends radially outwardly of the flat portion to effectively seal and abut against one or more seals or gaskets.