Tagged: 0 Thread(s). Quoted: 0 Post(s). The Prius gas tank is fitted with an internal bladder to prevent gas fumes from leaking into the air. It does create the problem of inconsistent gasoline fill-ups. 1 - The back pressure from the tank can cause early shutoff of the nossle. (don't overfill as gasoline can spurt out due to bladder pressure). 2 - In cold weather, the bladder gets stiff reducing the effective tank capacity. As was stated before the nominal tank capacity is 11.9 gallons.