The behavior of a drop cloud in thermocapillary motion in zero gravity is examined for both mono-dispersed and poly-dispersed cases. Numerical simulations of the thermocapillary motion of two- and three-dimensional fully deformable light drops are presented. The Navier-Stokes equations coupled with the energy conservation equation are solved by a front-tracking/finite-difference method. The material properties of the drop fluid and the ambient fluid are different, and the interfacial tension depends on the temperature. At moderate Reynolds (Re) and Marangoni (Ma) numbers, the results show that drops form layers nearly perpendicular to the temperature gradient. (c) 2006 Elsevier Ltd. All rights reserved.