Abstract: A method and device for leak testing vessels such as fuel cells or tanks which are large enough for a person to move around within holding a small hand held ball or balloon type device which is provided with a large aperture. In leak testing a vessel, the aperture portion of the device is pressed against the inside wall of the vessel with sufficient pressure to form an airtight seal between the inside of the device and the wall. While maintaining the airtight seal, the device is moved over the full inside surface of the cell. If there is a hole in the cell, the device which is very compliant will tend to collapse as it passes over the hole due to a resilient pressure drop created by the hole allowing the air to escape from the device to the atmosphere.