An absorption process for separating a feed gas stream having components with a spectrum of volatilities including volatile (light) components, intermediate volatility components, and least volatile (heavy) components. The disclosed process includes the steps of: (1) contacting the feed gas stream with an internally generated liquid lean solvent stream in an absorber to produce a light product gas stream that is composed of predominantly light components and a rich solvent stream containing most of the intermediate and heavy components; (2) flashing the rich solvent stream at reduced pressure in a flash zone to produce an intermediate product gas stream composed predominantly of intermediate components and a lean solvent stream; (3) conveying the lean solvent stream from the flashing zone to the absorber, wherein the lean solvent is composed predominantly of heavy components supplied from the feed; the process does not use an external lean solvent. The process is particularly useful for rejecting nitrogen from natural gas and for recovering hydrogen from refinery and petrochemical process offgases.