The paper describes two 2D steady-state models for solid oxide fuel cells (SOFC) with planar and tubular geometries fuelled by methane. Following a description of the basic geometries and general premises the approaches, assumptions and simplifications for the calculation of ohmic resistance, convective, conductive and radiative heat transfer are given. The modeling approach of the chemical reactions and molar and thermal balances are depicted in detail with the intention to allow for reproduction of the models. The required boundary conditions and input parameters of the models are also discussed. Relying on models, a bottoming GT cycle is introduced and specified and a base case for operation defined. The influence of pressure ratio, air inlet temperature, air flow rate and anode gas recycling are investigated in a parameter study. For both designs air flow rate and pressure ratio are the most important parameters considering the system performance, but for the tubular system these parameters have less impact than for the planar design. Based on the parameter study, a near-optimum case is defined specifically for both systems and the conditions in the fuel cells are investigated. The cycle balance is different in both systems, as the tubular fuel cell requires a lower air inlet temperature. Both fuel cell systems achieve above 65% electric efficiency. (c) 2004 Elsevier B.V. All rights reserved.