Regenerative intensifier systems that can receive fluids from landfills, anaerobic digesters, wastewater treatment plants, animal waste lagoons, swamp gas, decaying permafrost, and oceanic clathrate decomposition interchangeably with natural gas and other available fuels and substances and provide suitably conditioned fuel for operation of an engine, fuel cell, or other industrial and/or chemical processes. Alternatively, gases collected from landfills, waste digesters, bakeries, breweries, ethanol plants, calciners, power plant stacks, electrolyzers, and/or natural gas that may be delivered at relatively low pressures can be converted to high pressure and/or high purity constituents to enable efficient utilization as a transportation fuel and/or industrial feedstock or chemical plant reactant.