A ball valve for controlling fluid flow comprises a housing with a chamber therein and a fluid flow passage therethrough having an inlet and outlet portion to and from the chamber adjacent the lower end of the housing. An opening in the upper end of the housing communicates with the chamber and is sealed by a bonnet which is removably fastened to the housing and has a passage therethrough. A ball member is rotatably seated in the chamber and has a spheroidal lower portion with an anticlinal shaped fluid flow passage therethrough which intersects its axis of rotation. Valve seats are removably seated in the chamber about the inlet and outlet portions of the flow passage and have concave surfaces which seat the ball member and seal about the flow passage therethrough. The opening in the housing is cooperatively dimensioned with respect to the ball member and the valve seats to permit their removal therethrough. The upper portion of the ball member is operatively connected through the passage in the bonnet to an element for rotating the ball member about its axis of rotation between the open and closed positions.