The paper presents the results of numerical simulation of fluid flow in a rectangular room when fluid is supplied from two opposing slotted holes. The Reynolds number (Re) based on the height of the supply opening was varied from 20 to 140. For the given ratio of the lengths of the sides of the room, intensive self-oscillations developed due to instability arising when the supply jets interacted at Re ≥ 50. Already at a value of Re = 100 the flow became chaotic with a continuous frequency spectrum. The Strouhal number values corresponding to the main frequency of the oscillations depended weakly on Re and were approximately 3·10−3.