If you wanna nit-pic over oxygen...the beergun has the actual valve at the tip so that when you pull the botlle away the tube won't drain and fill with air. Sure it may have a purge, but first it has to evacuate the O2 from the fill tube each time. I've got the ball-lock adapter for my Nukatap and I can plug my beer gun into that and fill my bottles over a more spill-friendly surface than the top of my kegerator...if you're filling more than a 6-pack, that drip tray will over fill, plus; there's no room on my kegerator to set my capper down.