These 4oz CO2 tanks are great for anyone "keepin' it real" with a pump or stock class type paintball gun. The small, compact 4oz size is great for anyone wishing to carry a little extra air without the weight and bulk of a larger tank. It also makes a great reusable alternative to those one-time use "spare" tanks. Please note: By law, we are required to ship all CO2 and HPA tanks empty. Tanks will need to be filled prior to use.