The oscillatory phenomena in natural confection of low-Prandtl-number fluids were studied numerically in a rectangular cavity with horizontal temperature gradient at Prandtl number Pr = 0.01, aspect ratio A = J, 2, or 4, and Rayleigh number Ra = 104, 10s, or 106. In the case of A = 1 a main strong round roll cell was formed at Ra = 104. However, at Ra = 105and 106, two secondary roll cells in the core of a main roll cell were formed and rotated around the center of the system. The flow was oscillating. In the case of A = 2, i.e., a taller regime, the shape of the main roll cell varied with time at and above Ra = 104, and then the secondary complicated weak roll cells were formed above and below the main roll cells. This resulted in oscillatory phenomena even at Ra = 104. In the case of A = 4, three main roll cells were formed. At Ra = 105, secondary roll cells were formed between the main roll cells and then oscillation of flow occurred.