A ball valve (10,100) positioned between a first line and a second line, comprising: a housing; a ball (16, 104) disposed within the housing and having a bore, wherein the ball is configured to rotate between an open position and a closed position; an annular seat (38, 102) disposed between the housing and the ball, (16, 104) wherein the annular seat comprises: a first surface area exposed to a cavity pressure in the valve cavity and a second surface area exposed to a line pressure in the first line; a first annular sealing ring (42, 108) extending circumferentially about a radially-outer surface (44, 110) of the annular seat (38, 102) and configured to form an annular seal between the radially-outer surface (44, 116) of the annular seat (38, 102) and the housing in between the valve cavity and an annular space between the annular seat and the housing and block fluid flow from the valve cavity to the annular space; and an axially-extending passageway (46, 112) extending through the annular seat (38, 102) to enable fluid flow from the valve cavity to the annular space between the annular seat and the housing, characterised in that: the first surface area is at least 10 percent greater than the second surface area, the first surface area, the second surface area, and the first annular sealing ring enable an increase in pressure in the cavity of the ball valve acting on the first surface area to move the annular seat (38, 102) away from the ball (16, 104) as the ball rotates from the closed position toward the open position, and fluid flow from the valve cavity through the axially extending passageway (46, 112) into the annular space -increases pressure in the annular space, thereby eventually causes pressure balance across the annular seat (38,102) and enables the annular seat (38, 102) to move back towards the ball (16, 104). a housing; a ball (16, 104) disposed within the housing and having a bore, wherein the ball is configured to rotate between an open position and a closed position; an annular seat (38, 102) disposed between the housing and the ball, (16, 104) wherein the annular seat comprises: a first surface area exposed to a cavity pressure in the valve cavity and a second surface area exposed to a line pressure in the first line; a first annular sealing ring (42, 108) extending circumferentially about a radially-outer surface (44, 110) of the annular seat (38, 102) and configured to form an annular seal between the radially-outer surface (44, 116) of the annular seat (38, 102) and the housing in between the valve cavity and an annular space between the annular seat and the housing and block fluid flow from the valve cavity to the annular space; and a first surface area exposed to a cavity pressure in the valve cavity and a second surface area exposed to a line pressure in the first line; a first annular sealing ring (42, 108) extending circumferentially about a radially-outer surface (44, 110) of the annular seat (38, 102) and configured to form an annular seal between the radially-outer surface (44, 116) of the annular seat (38, 102) and the housing in between the valve cavity and an annular space between the annular seat and the housing and block fluid flow from the valve cavity to the annular space; and an axially-extending passageway (46, 112) extending through the annular seat (38, 102) to enable fluid flow from the valve cavity to the annular space between the annular seat and the housing, characterised in that: the first surface area is at least 10 percent greater than the second surface area, the first surface area, the second surface area, and the first annular sealing ring enable an increase in pressure in the cavity of the ball valve acting on the first surface area to move the annular seat (38, 102) away from the ball (16, 104) as the ball rotates from the closed position toward the open position, and fluid flow from the valve cavity through the axially extending passageway (46, 112) into the annular space -increases pressure in the annular space, thereby eventually causes pressure balance across the annular seat (38,102) and enables the annular seat (38, 102) to move back towards the ball (16, 104). the first surface area is at least 10 percent greater than the second surface area, the first surface area, the second surface area, and the first annular sealing ring enable an increase in pressure in the cavity of the ball valve acting on the first surface area to move the annular seat (38, 102) away from the ball (16, 104) as the ball rotates from the closed position toward the open position, and fluid flow from the valve cavity through the axially extending passageway (46, 112) into the annular space -increases pressure in the annular space, thereby eventually causes pressure balance across the annular seat (38,102) and enables the annular seat (38, 102) to move back towards the ball (16, 104).