P-GRADE portal is a multi-grid portal that can support GT2, LCG and gLite based Grid systems. In order to enable MPI execution in a transparent way in any of these grids we have developed a generic MPI execution mechanism that can tolerate the lack of shared working directory and is able to work with local job managers unable to support MPI jobs. The solution can support both direct job submission to selected grid sites as well as broker-based job submission. In case of using the EGEE broker the developed method enables the access of remote files stored in storage elements even if the executable code can access only local files