The influence of melt pool behavior on the competition between the nucleation of crystalline solidification products and glass formation is examined for an Fe-Si-B alloy. High-speed imaging of the melt pool, analysis of ribbon microstructure, and measurement of ribbon geometry and surface character all indicate upper and lower limits for melt spinning (MS) rates for which fully amorphous ribbons can be achieved. Comparison of the relevant time scales reveals that surface-controlled melt pool oscillation may be the dominant factor governing the onset of unsteady thermal conditions accompanied by varying amounts of crystalline nucleation observed near the lower limit. At high rates, the influence of these oscillations is minimal due to very short melt pool residence times. However, microstructural evidence suggests that the entrapment of gas pockets at the wheel-metal interface may play a critical role in establishing the upper rate limit. An observed transition in wheel-side surface character with an increasing MS rate supports this contention.