I think that -r8 is supposed work, but with gfortran 02-20 on the macintosh -
[dranta:~/tests/gfortran] dir% gfortran -i8 -r8 -o test test.f gfortran: unrecognized option '-r8' [dranta:~/tests/gfortran] dir% cat test.f program main stop end -- Summary: gfortran: unrecognized option '-r8' Product: gcc Version: 4.0.0 Status: UNCONFIRMED Severity: normal Priority: P2 Component: fortran AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: dir at lanl dot gov CC: gcc-bugs at gcc dot gnu dot org GCC host triplet: powerpc-apple-darwin7.8.0 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20144