A method of providing a source of breathable humidified oxygen gas. A membrane oxygen humidifier is provided that includes at least one water permeable membrane and an enclosure. The at least one water permeable membrane has a first membrane side and a second membrane side that are in communication through the water permeable membrane. The enclosure extends over the second membrane side and wherein the enclosure has an air inlet port and an air outlet port. A first gas containing oxygen is directed past the first membrane side. The second gas is directed past the second membrane side with a fan. The first gas is humidified by transferring moisture through the at least one water permeable membrane from the second gas to the first gas.
