An apparatus (10) and method for delivering a high partial pressure of a gas into a liquid. The apparatus has a gas transfer device (12) with a housing (14) that includes upstream (16) and downstream regions, between which there is located a gas-liquid contacting region (20) with contacting members (22), such as hollow microporous fibers. A reservoir (36) of gas supplies the gas at a high pressure (P) to a flask (38) of gas-depleted liquid and to the gas transfer device (12). The reservoir (36) of gas provides hydrostatic pressure for urging the liquid through the contacting members (22) and propelling the gas around the contacting members (32) so that the gas does not diffuse across the contacting members (22). The gas-enriched liquid is then ducted to a high resistance delivery channel (44) for administration to a site of interest without effervescence, bubble formation, or significant disruption of laminar flow.