An implantable penile prosthetic includes a pump attachable between a reservoir and a cylinder that is implantable into a corpora cavernosum of a penis. The reservoir has a central longitudinal axis and includes a wall connected between a first edge of a first surface and a second edge of a second surface. The first surface is concave relative to the first edge and the second surface is concave relative to the second edge such that each of the first and second surfaces form a depression in the reservoir when the reservoir is empty of liquid. The reservoir expands to contain liquid such that the first surface and the second surface are both convex relative to the central longitudinal axis.
