The stability of a two-layer return thermocapillary flow in the presence of an inclined
temperature gradient is investigated. Both a linear stability analysis and nonlinear simulations
have been performed for an air–water system. It is found that a rather weak
deviation of the mean temperature gradient from the vertical direction suppresses
Pearson's instability mechanism and leads to the appearance of oblique hydrothermal
waves. In a certain region of parameters, transverse convective rolls drifting with the
mean flow appear.