A ball valve structure having a ball member with upstream and downstream circular edge portions defining the entrance and exit ports of the ball member which ports are positioned adjacent the upstream and downstream seat members. Each of the circular edge portions has a generally arcuate groove or indentation therein positioned on the circumferential segment of the respective circular edge portion initially clearing the adjacent associated seat member upon rotation of the ball member from a fully closed position thereby increasing substantially the flow area exposed to fluid flow upon the initial opening of the valve member.






