A few years ago when I first started looking for a plasma torch, I came across a used Miller Spectrum 375 down at the LWS. I asked how much for the unit. It was being sold on consignment for $1400.00. It had only been used once and the guy didn't like it. So, he was trying to resale the unit back through the LWS where he had purchased it.

This is what he was trying to do with it. He was cutting thin sheet metal steel, like one would use for flashing, duct work, or light galvanized tin that you might use on a shed or barn. Whether he cut one sheet or several sheets at a time, he could not get the cut quality he was looking for, nor the increase in speed that plasma would offer. He was not using an air compressor, he was using 220 CF bottle with either compresses air and even used Compressed Nitrogen Gas in a bottle. Even though the bottle was at 2200 PSI when full, and properly regulated to provide the correct CFM and Input Pressure to the Miller 375 Cutter, it would not cut very long before using the contents of the nitrogen bottle up. He even tried using more cylinders in combination to get longer cuts, it still didn't work.

Your best bet is with a continuous air source, such as an air compressor. Just make sure you have the right PSI and CFM for your plasma cutter and make sure that air is clean and dry.

The Oxygen systems mentioned by others responding are more industrial in scope, not portable what so ever. Look at the industrial systems over at Hypertherm on their website, the oxygen systems don't look very portable, the machines are large and heavy, and the actual equipment runs on 400-600Volt 3 Phase power.