Contemporary Technical opinion is that a second generation Supersonic Transport will need to be commercially viable and meet environmental noise and emissions.Rolls-Royce and SNECMA have identified that engines with large variability (Flow Multiplication) will be needed. Two engine designs have been developed for this requirement and their characteristics identified. Both potentially reduce the cruise fuel consumption by up to 10% from that of the Olympus in Concorde and the subsonic fuel consumption by better than 15%. All this with some 35 to 45% improvement in thrust weight ratio. These two designs are a Tandem Fan system and MCV99 Mid Fan system and the essential difference is a trade of weight and friction drag due to the larger intake, nacelle and nozzle of the one, versus wave drag due to a larger maximum cross section of the other.