Compressed air is a big advantage over co2. You're shots will be far more consistant and your gun will be kept cleaner. It costs more because its better. A standard HPA tank size is 68/4500. 68 means its 68 cubic inches. 4500 means it can be filled up to 4500 psi.

Also, you need to cut down the size of your signature. If you click on the Uber FAQ sticky at the top of the new players forum you will find info on sig sizes and compressed air.  

Alright First off Please resize your sig, 350x150 pixels is the limit here.

HPA Stands for High Pressure Air, it is pretty much breathing air compressed to extreamly high pressures(3000 or 4500psi).

HPA is better than CO2 for the following reasons:

1. HPA doesn't Freeze up like CO2 does, allowing higher rates of fire for longer amounts of time.
2. HPA is more consistant than CO2. Therefore your input pressure is more consistant preventing Velocity Spikes.
3. HPA will not messup the internals of higher-end markers
4. HPA can be used in any tempeture, it is not affected by the weather like CO2 is.

HPA tanks cost more because 1. Most of them are made of Carbon Fiber, a very expensive material to make. 2. They have built-in regulators to lower thier pressure from 3000, or 4500psi to a pressure that your marker can handle. a HPA tank regulator without the tank runs in the range of $70.

HPA

You can switch Between HPA and CO2. You don’t need any modifications to the marker to accept a HPA tank, as long as it is a high output (more than 800psi) screw-in tank. Expansion Chambers do not help HPA at all, but don’t harm it either, you can leave you Exp. Chamber on your marker with no difference in performance. Regulators help keep the input pressure of your marker consistent, therefore preventing pressure inconsistency. Regs are not necessary for HPA, but can help out a lot.

rednekk98 wrote: Your signature is entirely too large. HPA is better than CO2 because it's always a gas, so you don't get velocity spikes and drops like you do when liquid cCO2 gets into your gun, it's also regulated for consistancy and less affected by temperature. It's also not as tough on your seals as CO2 and will help your internals last longer. Iy's totally necassary in high end guns. It's more expensive because of the technology. Tanks need to have a built in regulator to reduce the output pressure to safe levels, tanks also have to be able to take higher pressure than CO2 tanks, so they're a bit tougher I guess, and probably made to higher standards. If you want a tank with a high flow valve that won't give you shoot down on long stings, you will pay more. If you want a higher pressure tank like a 4500psi, you will pay more. If you want a lighter, carbon fiber wrapped tank, you will pay even more. Figure 10 shots per cubic inch at 3000psi and 15 per with 4500psi. A good sized tank is one that provides you with enough air for your needs, and feels right. With your drop, you may not be able to use a stubby tank. Use the above guid to figure ou how many shots you can get and figure out how much air you need, then look at the price factor. You'll need a tank with a high pressure(800-850psi) for your needs. And remember, when choosing your tank size, if you are playing at a field, you can get it topped off without it having to be empty like a CO2 tank. You can even have it filled while it's on your gun. That, and usually shorter lines for fills are yet more advantages with HPA tanks.

exactly