A balloon system is disclosed for positioning a distal end of a catheter at a treatment site. The system includes an elongated catheter shaft that is formed with a lumen and a tubular shaped balloon membrane that is made of a compliant material. For the system, the proximal and distal ends of the balloon membrane are affixed to an outer surface of the shaft to establish an inflation chamber between the balloon membrane and the outer surface of the shaft. The balloon membrane can have a non-uniform thickness between the proximal and distal ends of the membrane to establish a selected membrane shape when the balloon is inflated. For example, the selected membrane shape can be a prolate spheroid. With this arrangement, a relatively short and a relatively flat inter-contact surface in the midway region of the membrane is obtained when the balloon is inflated.
