An article of footwear with an upper and a sole structure secured to the upper may include one or more fluid systems with a pump chamber and a pressure chamber located adjacent to and below the pump chamber. In one configuration, at least a portion of a fluid within the pump chamber is separated from a fluid within the pressure chamber by a single layer of a polymer material. The fluid system may also include a fluid path extending between the pump chamber and the pressure chamber, and substantially all of the fluid path may be located between the pump chamber and the pressure chamber. In another configuration, at least one-half of a volume of the pump chamber may be located above a highest point of the pressure chamber.