An experimental and numerical study has been made of oil-water core-annular flow in a horizontal pipe with special attention for the turbulence in the water. An experimental set-up was built to be able to compare numerical predictions with detailed experimental results. The oil density was considerably smaller than the water density. Full 3D and time-dependent numerical simulations of some of the experiments were done. Only when a turbulence model is applied the agreement with the experiments is reasonably good.