Oscillatory thermocapillary flow experiments were conducted in microgravity. Silicone oil was placed in cylindrical containers and heated at the center by a CO, laser beam. The main objectives were to determine the onset of oscillatory thermocapillary flow and to study the important features of the oscillatory flow. Numerical and scaling analyses were also performed to understand the basic steady flows. The onset conditions show that the oscillation phenomenon cannot be explained if the fluid-free surface is assumed to be undeformable, Therefore, a parameter representing free surface deformation is derived. The oscillation patterns and frequencies ape also presented.