Fuel sensitivity experiments form an important feature of testing solid oxide fuel cell systems. In this paper we describe a fuel sensitivity test and its relation to fuel utilization. The sensitivity of the measured terminal voltage of a tubular solid oxide fuel cell to the fuel utilization provides important information about 'leaks' through the cell. Such leaks could arise from pinholes in the electrolyte or from other sources. First a simple analytical model is presented which is then refined using a numerical simulation. Such tests also provide a methodology to quantify the leaks present in the cell which can ultimately have an effect on fuel cell efficiency. (C) 2003 Elsevier B.V. All rights reserved.