Abstract. Expression templates (ET) can significantly reduce the implementation effort of mathematical software. For some compilers, especially for those of supercomputers, it can be observed, however, that classical ET implementations do not lead to optimal performance. This is because aliasing of pointers in combination with the complicated ET constructs is much more difficult. Therefore, we introduced the concept of enumerated variables, which are provided with an additional integer template parameter. Based on this new implementation of ET we obtain a C++ code whose performance lies very close to the handcrafted C code. The performance results of these so-called Fast ET are presented for the Hitachi SR8000 supercomputer and the NEC SX6, both with automatic vectorization and parallelization. Additionally we studied the interworking of Fast ET and OpenMP on a High Performance Opteron Cluster.