Or you can write it our in fortran without control words by either open(1,file='outfile',form='unformatted',recordtype='stream') which doesn't work on all machines (they don't recognize 'stream') or open(1,file='outfile',form='unformatted',access='direct',recl=RECL) but the later requires the RECL in 4-byte words on some machines, in bytes on others -Mike