A process for filling a gas tank made from a gas tank material with gas is provided, which process comprises the following steps: a) setting (S10) a nominal gas filling rate such that the tank is substantially completely filled within a predetermined filling time from a predetermined initial gas pressure value, b) determining (S20), assuming hot case tank conditions, a maximum mass-averaged gas filling temperature that will be reached at the end of the filling process, when filling the gas tank for the predetermined filling time with the nominal gas filling rate, c) selecting (S30) a target gas filling temperature not greater than the maximum mass-averaged gas filling temperature, d) cooling (S40) the gas to be supplied to the gas tank to the target gas filling temperature, e) starting the supply of gas to the gas tank, f) determining (S50) the actual mass-averaged gas filling temperature of the gas supplied to the tank, g) estimating (S60) an end-of-fill gas pressure from the actual mass-averaged gas filling temperature assuming cold case tank conditions, and h) terminating (S70) the supply of gas to the gas tank when the actual pressure of the gas tank is equal to the lower of the end-of-fill gas pressure and a maximum final fill pressure.