Liquid in a Petri dish spontaneously circulates in a radial pattern, even when the dish is at rest. These fluid flows have been observed and utilized for biological research, but their origins have not been well-studied. Here, particle-tracking to measure velocities of radial fluid flows, which are shown to be linked to evaporation, is used. Infrared thermal imagnn was used to identify thermal gradients at the air -liquid interface and at the bottom of the dish. Two-color ratiometric confocal imaging was used to measure thermal gradients in the vertical direction within the fluid. A. finite-element model of the fluid, incorporating the measured temperature profiles, shows that buoyancy forces are sufficient to produce flows consistent with the measured particle velocity results. Such flows may arise in other dish or plate formats, and may impact biological research in positive or negative ways. (C) 2016 American Institute of Chemical. Engineers