An experimental investigation of diffusion flames spreading along thin solid fuels in concurrent and opposed configurations in a gravity induced flow is presented in this study. Flame spreading over one side as well as on both sides of the fuel is studied. MATLAB is used to post process high definition flame videos to obtain flame spread rate as a function of inclination angle of the fuel surface, number of fuel sheets and separation distance. For one side burning, present results are compared with those from literature. For double side burning, the inclination angle is varied from 90 degrees (upward spread) to -90 degrees (downward spread), measured with respect to the horizontal (0 degrees). The spread rates in double side burning are higher and the maximum spread rate is observed for 90 degrees case, as opposed to 120 degrees in single side burning. The upward flame spread displays a non-uniform temporal variation, especially when the orientation angle is greater than 20 degrees. Fuel cracking was noted to be most severe at 90 degrees. However, the downward flame spread rate is almost steady. The multiple fuel sheets (2 and 3 sheets) are kept parallel to each other with the separation distance between them varied from 0.5 to 3 cm. In upward flame spread, for a small separation distance of 0.5 cm, multiple sheets produce spread rates lower than the single fuel case due to insufficient oxygen supply. At 1.5 cm separation, maximum flame spread rate is observed for multiple sheet cases, due to increased availability of oxygen and enhanced heat transfer from neighboring flames. At 3 cm, the spread rate is almost the same in all cases indicating that the interference effects have become weaker. The variation of flame-spread rate in multiple fuel sheets with respect to inclination angle is almost similar to that of single sheet cases. (C) 2015 The Combustion Institute. Published by Elsevier Inc. All rights reserved.