NOVELTY - The unit has an aperture (42) extending between an upper face (40) i.e. outer/external face, and a lower face (41) i.e. inner/internal face. Circumferential ridges (43) surround the aperture on the upper face. A channel (46) is placed between each adjacent pair of circumferential ridges. A flat seal/ flat profile region (50) is placed on the upper face peripheral to the circumferential ridges, where the flat seal occupies a different plane than the plane occupied by apexes of the circumferential ridges and the circumferential ridges occupy different planes.    USE - Resilient sealing unit for use in an interface seal assembly of a fuel cartridge i.e. refillable fuel cartridge, utilized for producing and storing gaseous/fluid fuel for fuel cell apparatus (all claimed) i.e. electrochemical fuel cell apparatus, for portable electronic equipment e.g. laptop computer, tablet computer and mobile telephone.    ADVANTAGE - The concentric circumferential ridges can increase stiction forces between the cartridge and the fuel consuming apparatus, such that presence of the channels 48 between the compressible ridges can provide a suction force when air is expelled from the channels during compression of the sealing surface onto the fuel consuming apparatus pressure plate, thus improving retention forces and resisting disturbance of the seal during vibration and flexing. The unit utilizes multiple concentric circumferential ridges as sealing surfaces to reduce reliance on a single sealing boundary such that the resilient sealing material can be made harder, and less prone to damage than a sealing surface reliant on a single knife edge seal, so that compression force required to attach the cartridge to the fuel consuming apparatus can be reduced if a soft resilient material is used with multiple concentric circumferential seals.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) a method for reconditioning a fuel    (2) a fuel cartridge    (3) an interface seal assembly.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of an interface seal assembly in a cross section.    Upper face of unit (40)    Lower face of unit (41)    Aperture (42)    Circumferential ridges (43)    Channels (46, 47, 48)    Flat seal/ flat profile region (50)