Abstract: A method for detecting a leakage in a fuel tank system includes setting a first reference pressure value and generating an initial pressure in the fuel tank system, as well as determining a pressure difference between the pressure in the fuel tank system and the first reference pressure. The method also includes determining a linearity metric by comparing the determined pressure difference to at least one out of a linear and a non-linear data model, the linearity metric quantifying the non-linearity of said pressure difference as a function of time, and detecting a leakage in the fuel tank system based on the linearity metric, where a non-linear pressure difference function of time is indicative of a leakage in the fuel tank system.