I have not used CO2, but I started with scuba tanks. Same principle. A tank prefilled with a lot of air. I was running 80 cu ft cylinders at 3,000 psi. I had enough air to paint all day and plenty on demand no matter what pressure I run my airbrush at. It really is nice. I'm now trying to get use to an airbrush compressor. I hated it at first, but then made a tank for it and it is ok, but not as nice as running off a tank.

The down side to running off of a tank (CO2 or other), is that you have to get them filled. This can be a problem if you need to get one filled right away and there is no place open to fill them. While working Daytona Beach Bike week, I met and got the cell number of the local scuba shop owner so that I could get my tanks filled even if he was closed.

If you decide to use a CO2 tank, I would recommend getting two so that when you run out, you can switch tanks and finish what you are working on. Another option is to get one tank and an airbrush compressor as a backup, but going from the tank to the compressor will drive you crazy.

Hope this helps. If you have any specific questions, I'll try to answer them. If I can't, I'm sure there is someone else here that can.
Hey Krone how long would those tanks last you? I was always curious what a 20lb tank at 3000 psi translated into. Wish I could get the 80lb tanks we had in the Army for nitrogen for filling up stuff on the flight line, we had those suckers at 6,000 psi, bet that would last a good while.
Its not about the psi. Its the volume. My tanks filled to 3000 psi equaled 80 cubic foot of air. They would last me all day at an event doing tattoos and body painting.

As far as the 20lb CO2 tanks, I don't know what 20lbs translated into as far as volume. If you could find the Cu ft or gallons I could help you figure it out. Also, most of the CO2 tanks I'm seeing are only 1800 psi. Dimensionally they are about the same as an 80 aluminum for scuba. So at 1800 psi they should be approximately 48 cubic feet. So I would say about 45 minutes of continuous spraying. Continuous spraying, meaning pressing the trigger and holding it down the whole time, which you don't do while painting. Depending on the type of painting your doing and how fast, I would guess between 1-4 hours of painting. I think my 80s lasted 6-8 hours doing tattoos and body painting. The more you hold the trigger down and the higher your pressure at the airbrush, the faster you will go through your air. 20 psi uses twice the air of 10 psi. I was figuring 1 cfm for your airbrush which is probably really high Another factor on your air supply is the size of the needle. Larger needles use more air at the same psi. There is a lot to consider when trying to determine how long a tank will last.

If you knew how many cfms your airbrush used at a given pressure and the cubic foot capacity of the tank at full pressure, you could find the continuous spray time at that pressure which would be the minimum. You actual time would be a lot longer. In a 5 minute period of painting, how long do you have air going through your airbrush? If you paint for 5 minutes but only press the trigger for two minutes, you will get more than double the continuous time.

With all of the variables, that is why it is good to have a back up, especially if you are in a situation where running out of air is not an option. I always keep a back up on hand. At one event, I had a full tank the night before, but it was empty in the morning. I left the valve on and my regulator had a small leak. I have also had a tank run empty in the middle of a body painting. You can't tell the customer to sit there for a few hours while you go to get air.

CO2 tanks are nice though. They are silent and you have plenty of volume at your airbrush so long as you have air in the tank. Think about your painting situation and needs. Will this be the best option for you or would a compressor suit you better?

This is a lot and I'm tired, so it may not make much since and I probably repeated myself, but there is no absolute answer.
Thanks guys..first of all I know that CO2 is anhydrous so no moisture trap needed. Second..I'm a modeller so the subjects I'm working with are small so the airbrush is not used for long periods of time. In a modeling forum I read that a tank would last a year. This makes sense seeing that it can take months to complete a model. I was really just curious to see if anyone on here has used it and how they like it. I have a small tanked compressor but I don't really like it..thanks for the feedback.
For what you're doing, I think the CO2 will be a great way to go. It will last you a long time and there is no noise.
I used to have CO2 as my prime source of compressed Air (or gas, really). Sure it works fine, and it's great for a portabel setup, but I do prefere a good compressor. I always worried about ending up empty in the middle of a session, or with the airbrush full of paint. It made me to airbrush less, only to save on CO2.
I would imagine that there's a guage setup out there that would show PSI therefore you would know when your close to empty.
The only way to really know, was to keep shaking the bottle now and then, to feel/hear how much was left.
The gauge went from full pressure to nothing in minutes when you got there...
Oh ok well that sucks..I'm sure I'll just stick with my compressor.
They do make regulators for them. Look at brewing supplies.
I have seen them..I may look into it in the future but for now the compressor we I'll do.