I've heard that nitrogen or N2/CO2 blend is preferred for stouts cause it gives a 'nicer' head. I do not keg-carb, yet, but working on it. If you wanna spring for a phone call, call the Dover, NH AirGas store; I think the Mgr's name is Scott, and ask him. They have a banner out on the main drag that says: 'Beer Gas' , so I guess they can help you.