Oscillatory fouling in condensers using cooling tower water was recognized in 1980s, but it had not yet been theoretically analyzed. Without careful theoretical analysis, it is easy to think that oscillatory fouling phenomenon is generated from experimental uncertainty. The new analysis is to split the fouling rate into a mean variable and a fluctuating variable. The mean variable exhibits an asymptotic behavior, and the fluctuating variable exhibits an oscillatory behavior. A theoretical analysis based on the relationship of continuity is used to present fouling oscillatory behavior along the space and time dimensions simultaneously to provide the intuitive understanding in physical mechanisms driving the phenomenon. A series of long-term cooling tower water fouling tests were conducted: fouling data collected in two copper helically ribbed tubes with the same internal and external diameters and different inside geometric parameters at the same water velocity in condenser in practical cooling tower conditions present oscillatory behavior. The frequencies of the fluctuation are the same for the two tested tube geometries. The spatial and the temporal oscillatory fouling behaviors presented in the experimental results are predicted by the theoretical analysis.