The propagation speed of tribrachial (triple) flames in laminar propane jets has been investigated experimentally under normal and micro gravity conditions. We found in the present experiment that the displacement speed varied nonlinearly with axial distance because the flow velocity along the stoichiometric contour was comparable to the propagation speed of tribrachial flame. Approximate solutions for the velocity and concentration accounting density difference and virtual origins have been used in determining the propagation speed of tribrachial flame and the concentration field was validated from the measurement of Raman scattering. Under the microgravity condition, the results showed that the propagation speed of tribrachial flame decreased with the mixture fraction gradient, in agreement with previous studies. The limiting maximum propagation speed under the microgravity condition is in good agreement with the theoretical prediction, ie, the ratio of maximum propagation speed to the stoichiometric laminar burning velocity is proportional to the square root of the density ratio of unburned to burnt mixture. (C) 2003 The Combustion Institute. All rights reserved.