This paper reports a new study where leakages through a seal in a solid oxide fuel cell (SOFC) button cell is investigated in detail. A 2D model is used to determine different flow characteristics of the leakages and its effects on the cell performance. The leakage effects on the performance are studied at different seal porosities, and other parameters are also investigated. The results of this investigation indicate that a seal leakage can affect the cell performance significantly if the leak comes from outside the test rig. That is, an air leak must be present through the seal and must flow into the anode chamber, where then it affects negatively the cell performance. In addition, the model developed here can be used to include leakages in stack modeling studies.