Determining the thermodynamic state of fuel includes opening the venting connection to release the tank pressure while monitoring the derivative pressure (dP/dt), closing the venting connection when one of the following conditions is met, the derivative pressure (dP/dt) is lower than a predetermined threshold DP1 or the opening time Δt1 reaches a predetermined value, if the closing of the venting connection occurs when the opening time Δt1 reaches the said predetermined value, determining that the fuel is boiling and aborting the method if the closing of the venting connection occurs when the derivative pressure (dP/dt) is lower than the said threshold DP1, measuring an initial tank pressure at the closing of the venting connection, measuring the final tank pressure after a closure time Δt2, calculating the pressure variation (ΔP/Δt2), comparing the pressure variation (ΔP/Δt2) with a first threshold PV1, if the pressure is lower then aborting the method.