A rotational gas bearing allows rotation about a single axis while supplying a pressurized gas through the bearing. The gas bearing includes a gas supply member and a gas sink member. A cylindrical depression is located in one of the gas supply member and the gas sink member. A cylindrical protrusion protrudes from the other of the gas supply member and the gas sink member and is sized to fit within a cylindrical depression with a predetermined clearance. The gas supply bearing surface is opposed to the gas sink bearing surface. An opening is located in the gas supply bearing surface. A porous coating covers a portion of the gas supply bearing surface surrounding the opening. The porous coating communicates with the pressurized gas supply via the gas supply member for maintaining a bearing pressure between the porous coating and the gas sink bearing surface, such that the bearing pressure is greater than the feed pressure. An annular channel located in the gas sink bearing surface is aligned with and located opposite the opening, and communicates with the gas sink via the gas sink member.