Hello, Is there a specific reason why PETSC_COMM_WORLD is not a PETSc communicator, i.e., has no Petsc_Counter_keyval attached? ierr = PetscOmpCtrlCreate(PETSC_COMM_WORLD,nthreads,&ctrl);CHKERRQ(ierr); yields [0]PETSC ERROR: Bad MPI communicator supplied must be a PETSc communicator [0]PETSC ERROR: #1 PetscShmCommGet() at src/sys/utils/mpishm.c:60 [0]PETSC ERROR: #2 PetscOmpCtrlCreate() at src/sys/utils/mpishm.c:340 Thanks, Pierre