I am using a 68ci 4500 air tank, it will not fit without ALOT of wiggleing! I ended up cutting the stiching off around the tank compartment and sewing in a strap along the outside to make the compartment bigger. but not my Air tank fits nicely all it needed was an inch.
It will fit a 20oz CO2 tank nicely, but some larger Air tanks will not fit.
Nice Harness, looks as if it will last a long time!