The formation of oil-in-water dispersions is a critical step during the blowout of coastal and deepwater oil and gas production systems, and is a determining factor in the vertical and lateral migration of oil through the associated adjacent water column. In this study a high-pressure sapphire visual autoclave apparatus was used to measure the size of crude oil droplets that were saturated with gas and dispersed in an aqueous phase as a function of mixing speed. Oil-in-water droplet size distributions were measured at pressures of 11 MPa, for autoclave stirring rates of 200-1000 RPM (1076 < Re-stirred (vessel) <= 5378). Arithmetic mean droplet diameters decreased monotonically from 344 to 125 mu m over this range, with maximum droplet sizes decreasing from 708 to 441 mu m. A model tuned to the measured oil-in-water data was used to predict a mean droplet size on the order of 80 mu m for Deepwater Horizon conditions; when incorporated into far field blowout simulations, this droplet size data enables quantitative assessment of the impact of dispersant injection at the blowout site. (C) 2015 Elsevier Ltd. All rights reserved.