Since ethylene/ethane separation by cryogenic distillation is one of the most energy intensive processes, it can be economically interesting to combine it with energy efficient membrane technology. The effect on the viability of different process configurations in relation to the ethylene permeance (2.8 x 10(-6)-2.8 X 10(-5) mol/(m(2) s kPa)) and ethylene/ethane selectivity (3-1000) of the membrane is investigated using Honeywell's Unisim Design Suite R390. Results are compared to conventional distillation. In addition, the membrane feed pressure, permeate pressure, and membrane surface area have been optimized to obtain the highest possible cost savings. It is concluded that the series configuration is the most beneficial with savings of 16% on the total annualized costs. Hybrid membrane-distillation technology is interesting for membranes having ethylene permeances and selectivities beyond 2.8 X 10(-5) mol/(m(2) s kPa) and 30, respectively. Increasing the membrane feed pressure toward its critical pressure (P-c = 4850 kPa) is always beneficial, and the optimal permeate pressure increases to 2050 kPa with increasing ethylene permeance. For material scientists, it is advised to focus on increasing membrane selectivity once an ethylene permeance of 1 X 10(-5) mol/(m(2) s kPa) is obtained, since higher permeances beyond this point yield less additional cost savings compared to increments in selectivity.