I also wanted to mention that I use to travel with both a Faber Castell rollerball and Lamy M21 ball pen refills. None EVER leaked the tiniest bit. My Montblanc fountain pen with MB ink did not leak, either in the rare trips I took it on. I did not consciously do anything to the ink level in the converter nor do I remember whether I carried it upright. It is also the small MB size. I never tried the big one with the piston filler on an airplane.