Abstract: A novel plug valve assembly is described having improved leak-resistance under high pressures. It includes a housing with inlet and outlet ports and a cylindrical valve chamber. Cylindrical valve sealing members are slidably mounted in the ports, each sealing member having a main body portion with a concave end face portion adjacent the valve chamber and an axial bore extending therethrough. The main body portion has an annular recess on the cylindrical surface thereof extending from the concave end to an annular abutment intermediate the length of the main body portion. A generally tubular resilient collar is slidably mounted on the recessed portion of the main body, this collar having a thickness substantially equal to the depth of the recess and having a concave end portion protruding beyond the concave end of the main body portion.