Gas supply arrangement of a marine vessel being adapted to carry liquefied gas in its gas tank having an ullage space section and a liquid phase section, which arrangement provides the gas for demands of the vessel, the arrangement comprising a gas supply line provided for delivering the gas formed in the gas tank to a consumption device, and a piping extending from the liquid phase section to the ullage space section of the gas tank being provided with at least a pump, for introducing gas into the ullage space section. The piping is provided with a heat transfer unit for effecting on the temperature of the introduced gas. The invention relates also to method of providing gas in a marine vessel with liquefied gas tank.