A pump having an increased energy efficiency is provided. The pump has an internal power fluid column and a transfer piston which is reciprocatingly mounted about the power fluid column. The transfer piston defines a product fluid chamber, located above the transfer piston valve, and a transfer chamber, located below the transfer piston valve. The power fluid column has at least one passageway, which allows the fluid inside the power fluid column to be in communication with a power fluid chamber. The power fluid chamber, the transfer chamber, and the product chamber are situated coaxially about the power fluid column.