Experimental and theoretical investigation of a recently patented down-hole direct-acting reciprocating pump system is presented. The technology, (US Patent No. 5,860,795) consists of operating a gas well with gas and liquid phases being produced separately by using the gas phase to power a pump to bring the liquid phase to the surface. This would increase the duration of profitability of many gas wells in North America. Experiments and modeling were used to determine optimum design parameters to maintain flow at a minimum reservoir pressure; an optimum area ratio for the gas liquid pistons is approximately 40. The effect of friction in the pumping system was predicted to have a small effect on this optimum design. The results of this investigation will now be used to design and construct a prototype for field testing.