Different schemes of connecting distillation lowers are examined: from separating subsystems with coupled heat flows to separating subsystems with linkages of towers for distillate or residue. The causes that prevent implementation of separation schemes with connected heat flows as subsystems with minimum power consumption for separation of multicomponent mixtures are revealed. A system is proposed for separation of crude oil as a multicomponent mixture into seven products with minimum consumption of primary energy resources due to maximum recovery and utilization of secondary energy resources. The use of combined separation schemes together with optimum subsystems for supplying and recovering thermal energy, will eliminate terminal coolers-after-coolers and cooling agents.