Recent SOHO/UVCS observations of the O5+ ion line emission at 1032Å in coronal streamers indicate that the emission is stronger by an order of magnitude at the edges (legs) of streamers than in the central core of streamers. In contrast, the brightness of the Ly‐α emission peaks in the core of streamers. I have developed the first 2.5D, three‐fluid numerical MHD model of the slow solar wind flow in a coronal streamer. Using the model I find that the enhancement of the oxygen line emission occurs due to the enhanced abundances of O5+ ions in the legs of streamer caused by the Coulomb friction with the outflowing protons. Thus, the enhanced O5+ emission traces the source regions of the slow solar wind in coronal streamers. The identification of these regions helps to understand the origins and the composition of the slow solar wind.