Membrane covered oxygen sensors, or Clark electrodes, are used for monitoring the concentration of oxygen in blood. The operation of such sensors is governed by the diffusion equation with different diffusion coefficients in different sub-domains. The form of the boundary conditions and the material interface conditions means that the derivative of the solution has discontinuities which restrict the convergence of standard numerical methods on regular meshes. We describe and computationally compare adaptive finite element methods based on continuous and discontinuous basis functions to overcome this problem. (c) 2005 Elsevier B.V. All rights reserved.