An operating gas system for an underwater vehicle, particularly for a submarine or an unmanned underwater vehicle, includes a fuel cell system and an operating gas vessel connected in terms of flow to the fuel cell system. In order to achieve simple and efficient storage of boil-off gasses, a gas-receiving device is also provided and is connected to the operating gas vessel. The gas-receiving device contains a sorbent for receiving boil-off gas from the operating gas vessel. The boil-off gas, which is produced in the operating vessel with an operating gas for the fuel cell system and which cannot be consumed directly in the fuel cell reaction, is therefore collected and stored with the aid of the sorbent in the gas-receiving device. A method for operating an operating gas system and an underwater vehicle are also provided.