This paper describes an approach for automatically generating optimized parallel code from serial Fortran programs annotated with high level directives. A preprocessor analyzes both the program and the directives and generates efficient parallel Fortran code that runs on a number of parallel architectures, such as clusters or SMPs. The unique aspect of this approach is that the directives and optimizations can be customized and extended by the expert programmers who would be using them in their applications. This approach enables the creation of parallel extensions to Fortran that are specific to individual applications or science domains.