When a fluid is oscillated vertically, under certain parameters, bubbles may move downwards instead of rising. Prior publications defined the threshold frequency as the frequency at which bubbles oscillate in a stationary state. Beyond the threshold frequency, however, bubbles move downwards. This paper investigated the hypothesis that the threshold frequency will increase as the density of the oscillating fluid increases. The parameters in this study were restricted to the frequency of the oscillating fluid and the density of the liquid. As the fluid density increased, the threshold frequency was measured to be higher. Our data analysis concluded that the threshold frequency is positively correlated to the density of the surrounding fluid.