The technical and economic feasibility of a hybrid separation process in which gas separation membranes are combined with conventional distillation are assessed for the separation of ethylene from ethane and of butadiene from a C-4-mixture. The potentials for increased energy efficiency and debottlenecking were determined in relation to the required membrane performances. The energy saving potential for the separation of ethylene from ethane is rather low owing to the required very high membrane selectivity. Energy savings can be expected when the membrane selectivity for ethylene is >60. However, the possibility to increase the column capacity in an existing plant by using a membrane is very high. This can become economically attractive if the membrane has a selectivity for ethylene of >= 10. In the case of butadiene separation, the energy savings can be as high as 30% depending on membrane selectivity and process configuration. This high value can be reached when the membrane selectivity for butadiene relative to saturated hydrocarbons equals 15. Again, an increase in the production capacity of butadiene can be achieved in an economic viable fashion.