The influence of stream concentrations and velocities on the flame shape in a multiple-port burner is theoretically and experimentally studied in this work. A general solution of normal and inverse diffusion flame configurations in a multiple-port burner is obtained with the inclusion of the effects of axial diffusion and unequal stream velocities. The theoretical results show that not only the flame height but also the flame shape is affected by the Peclet number. In the theoretical analysis, the fuel and oxidizer concentrations, stream temperature, and stream velocity are three important parameters. Flame configurations can be predicted well by including the temperature effect in calculating the Peclet number. For relatively weak (or strong) flame intensity, the prediction of flame configurations agrees well with the experimental results if a lower (or higher) temperature is used. In the experiment, different flame configurations are observed and discussed for various stream velocities and concentrations. The transition of inverse diffusion flame from a single cone-shaped flame to a double cone-shaped flame to an envelop flame occurs when the inner stream velocity is adjusted for fixed middle and outer stream velocities. It is of interest to note that under the same operating conditions the flame has a history-dependent configuration decided by increasing or decreasing the inner stream velocity.