A process for removing CO from a gas stream which comprises contacting the gas stream with a mixture of Cu.sub.2 O and oxalic acid in an inert organic solvent. The process selectively removes CO from the gas stream and forms a novel cuprous oxalate complex of the formula Cu.sub.2 (CO).sub.2 C.sub.2 O.sub.4. Cu.sub.2 (CO)C.sub.2 O.sub.4 can be further contacted with a feedstream containing unsaturated hydrocarbon L thereby displacing CO from the oxalate complex, removing L from the feedstream and forming a new complex Cu.sub.2 (CO).sub.n L.sub.m C.sub.2 O.sub.4 where n and m are numbers from 0 to 2.