A novel method is disclosed for treating a contaminated gas such as a contaminated natural gas or a synthesis product gas from the partial oxidation of petroleum or coal to concentrate and remove hydrogen sulfide at a reduced energy and capital requirement. Hydrogen sulfide in the contaminated stream is absorbed to form a hydrogen sulfide rich solvent which includes co-absorbed carbon dioxide, which is then removed to prevent dilution of the concentrated hydrogen sulfide formed when the solvent is regenerated. The solvent leaving the hydrogen sulfide absorber is heated before entering a high pressure stripper column wherein the co-absorbed carbon dioxide is stripped from the solvent, preferably by stripping with nitrogen or a portion of the product gas, and the carbon dioxide is recycled to the hydrogen sulfide absorber. The CO.sub.2 stripper is operated at a pressure not substantially below the pressure of the hydrogen sulfide absorber, eliminating the need for large compressors required in conventional methods to recycle the carbon dioxide.