A theoretical and experimental description of the lateral mode behavior in oxide-insulated stripe geometry lasers with stripe width below 8 μm is given. The analysis is based on the waveguiding effects of carriers injected into the active region, and includes accurate, self-consistent solutions to the waveguide and carrier distribution equations. In agreement with experiment, wide (geq12 mum) near-field patterns and non-Gaussian far-field patterns are found for the fundamental mode. As the current is increased above threshold, the near fields become progressively wider and the far fields develop a twin peak structure. The optical properties of the output are dominated by a one-dimensional analog of spherical aberration. It is shown that high pulsed output power may be obtained in fundamental lateral mode without incurring catastrophic facet damage.