Fouling of equipment surfaces affects the efficient processing of heavy hydrocarbons. An experimental study is reported on the deposition of bitumen-containing droplets from a gas-vapour mixture at temperatures up to incipient coking conditions. A heavy oil-diluent feed mixture was atomized with nitrogen in a vertical spray chamber, and flowed upwards normal to a circular disk. The disk was attached to a load cell to measure total deposited mass with time, and at the end of each experiment the amount deposited was determined gravimetrically. The effects on deposition rate of heavy oil concentration in the feed mixture, temperature, and flow-rates of feed mixture and nitrogen were determined. Different surfaces and coatings were tested. The deposition rate was found to depend most strongly on the droplet concentration, which was predicted with HYSYS, using an isothermal flash calculation. As temperature was increased, deposit H/C atomic ratio decreased and ash content increased.