[jjk166]

The concorde was woefully less efficient than modern aircraft but this wasn't because it flew supersonically but instead because it used turbojets. Modern aircraft use turbofans which are far more efficient. The concorde was actually designed to save fuel as supercruise is more efficient than transonic flight for a given engine. Unfortunately turbofans for supersonic flight weren't developed until the late 80s, by which point there was little demand for a new SST.