The rate of evaporation from the wetted floor of a tube open at the top to a relatively dry environment is investigated analytically, numerically and experimentally for the case of a light vapour. Though buoyancy forces ensure that the heavier external gas is always in motion, it is found that inside the tube both stagnation (diffusion-dominated evaporation) and convection are possible. In contrast to previous studies, axisymmetry of the postcritical flow is not assumed, leading to a reduction in the predicted critical Rayleigh number by a factor of 5 and much better agreement with experiment. (C) 2000 Elsevier Science Ltd. All rights reserved.