It depends on how ones defines efficiency. Some define it based on time to boil, pressurized stoves are generally faster. Some define efficiency as amount of fuel needed to achieve a boil, non-pressurized generally use less fuel to achieve a boil. I personally define efficiency as the the amount of heat available in the fuel converted to increase in water temp. Based on *my definition* the most efficient stove I have seen or used is the Zelp designed fancee feest, it is a wick stove. It converts almost 80% of available energy to the water temp. The Penny Stove, as a comparison doesn't break 50%. As Bill said, ones stove choice is dependent upon ones use of it and not some arbitrary metric. On my way to the alky stove anonymous meeting now.