A reservoir is described that is adapted to hold a liquid for transfer to and inflation of an implantable penile prosthetic. The reservoir includes opposed end walls, opposed side walls, and an opening that communicates with the implantable penile prosthetic through tubing. The reservoir has a first major surface formed between the opposed end walls and the opposed side walls that is located opposite from a second major surface formed between the opposed end walls and the opposed side walls. The first major surface and the second major surface are both concave. The first major surface is less concave than the second major surface.