A method and system are disclosed for pumping a multi-phase fluid from an oil well. The method may comprise delivering a flow of a multi-phase fluid to a multi-phase fluid pumping system, wherein the multi-phase fluid has a gas/liquid ratio that varies during operation. The multi-phase fluid pumping system is operated to increase the pressure of the multi-phase fluid that is delivered thereto. Thereafter the flow of pressurized multi-phase fluid is delivered from the multi-phase fluid pumping system to one or more discharge conduits. The pump system may have a pump fluid chamber between opposed pairs of buffer chambers and driving fluid chambers. Seals may be provided to seal the respective chambers.