We have investigated the atomisation of a thick liquid film by high speed co-flowing gas jet. The study is focused on the mechanisms controlling the drop spatial distribution downstream injection. These results are needed for properly initializing two-fluid euler-euler [1] or lagrangian [2] simulations. Measurements of the drop characteristics (concentration, velocity, size),available downstream injection, indicate that the spatial dispersion of the drops is related to their size, the smallest drops being more widely spread than the larger ones. However, the standard dispersion model based on turbulent dispersion is unable to describe such a behaviour up to a downtream distance about 6 Hg. According to the experimental results presented, the drawback may originate from the initial ejection conditions. Another origin could be a change in the gas structure (jet expansion, turbulent intensity) at short distances. The relatives contributions of these mechanisms needs to be quantified.