In Czochralski (Cz) crystal growth, the observed complicated melt flows are caused by different types of instability such as buoyancy-induced instability, Marangoni instability or baroclinic instability. In order to grow single crystals of large size and high quality, it is very important to strictly control these melt flows, and in particular to know which instability is dominant in such flows. Proper orthogonal decomposition (POD) is a powerful method to disclose the basic structures of complicated flows. It was traditionally used to analyze flow structures and, more recently, to construct low-order dynamic models able to reproduce complicated flows. An attempt to apply POD to analyze the flow instabilities was conducted in the case of the oscillatory melt flows occurring in an axisymmetric Cz configuration and caused by both buoyancy-induced and surface tension-induced instabilities. Direct numerical simulation was used to obtain the flow fields driven by both buoyancy and surface tension and also the flow fields driven by one of these forces alone. POD was then employed to extract the basic modes from the flow fields. By comparing the basic modes between these situations, the dominant instability involved in such complicated flows has been revealed. In addition, it was found that the basic modes corresponding to buoyancy-induced instability are global and rotating and those to Marangoni-induced instability are local and traveling. All these indicate that the POD could be a powerful method in instability analysis. (c) 2007 Elsevier B.V. All rights reserved.