A premixed flame in a tube suffers strong variation in its shape and structure depending on boundary conditions. The effects of thermal boundary conditions and flow fields on flame propagation are numerically investigated. This study employs eight combinations of thermal and velocity boundary conditions. Navier-Stokes equations and species equations are solved with a one-step irreversible global reaction model of methane-air mixtures. Finite volume method using an adaptive grid method is applied to investigate the flame structure. In the case of an adiabatic wall, friction force on the wall significantly affected the flame structure while in the case of an isothermal wall, local quenching near the wall dominated flame shape and propagation. In both cases, variations of flow fields. occurred not only in the near field of the flame but also within the flame itself, which affected propagation velocities. Near the quenching conditions, strong similarity in the flame structure was found regardless of the boundary velocity profiles due to self-induced velocity deformation. This study provides an overview of the characteristics of flames in small tubes at a steady state. (c) 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.