An electron-beam pumped KrF laser has been developed as a part of an assessment study of the KrF laser as an energy driver for inertial fusion reactor. As the result of a parametric study of the laser medium kinetics and several technical developments, it has been shown experimentally that high efficiency operation of the KrF laser is possible under a high excitation rate of some 1 MW /cm³, obtaining as much as 82 J of 249 nm output of 100 ns duration by an internal efficiency of more than 10 % and electrical efficiency of 2.5 % from an active volume of 6.2 litter.