Sharp (99% purity) separation of a ternary mixture, characterised by near uniformly distributed volatility, by direct separation sequence without, with forward, and with backward energy integration, by indirect separation sequence without, with forward, and with backward energy integration, by sloppy separation sequence with forward and with backward energy integration, and by thermally coupled sloppy separation sequence (Petlyuk system) is rigorously modelled and optimised. Three feed compositions, namely (Case 1) equimolar A/C ratio with 10% B, (Case 2) equimolar feed, and (Case 3) equimolar A/C ratio with 80% B are compared. Comparison is based on total annual costs (TACs) using European and American price systems. The savings in TAC of Petlyuk are uniformly about 28–33% in all the three cases, while the savings of the energy integrated systems increases together with increasing ratio of B in the feed. In Case 1, Petlyuk system is the winner, with 33% savings, but a conventional energy-integrated system is handicapped by just a very few percent. In Cases 2 and 3, Petlyuk system is not amongst the best structures. In Case 2, either the conventional energy-integrated systems or the energy-integrated sloppy structures win with 35–41%; while Case 3, the energy-integrated sloppy structures are the best with about 51% savings.