The paper presents the results of tests and analysis of hydrodynamics and heat transfer conditions of cocurrent annular gas-high viscous liquid downward flow in vertical pipes. Systematic of flow patterns and the range of their occurrence have been given. Selected values characterizing the nature of flowing liquid films of high viscosity have been characterized and described. The analysis of the influence of selected heat and flow parameters on transfer conditions has been made and dependences for calculating heat transfer coefficient in liquid film have been given.