Abstract: Improved methods and apparatus are provided for sealing at the uppermost end of a casing string to provide circulation from adjacent the lower end of the casing string and into a well bore to enable the casing string to be more easily lowered into the well bore. A casing circulator is provided for lowering into the uppermost end of the casing string above the rig floor, and for sealing with an interior surface of the uppermost end of the casing string. An external sealing member of the casing circulator may be moved axially with respect to an inner packer tube, thereby allowing the sealing member to become inflated while also enabling fluid to pass through the casing circulator and into the casing string. The techniques of the present invention may also be used to fill the casing string as it is lowered into the well bore.