An investigation of the downwind movement, distribution and distance covered from a spray source of insecticide to which oil is an additive. Vertical targets were placed at distances ranging from 0.25 to 64 m and at three heights, 35, 70 and 150 cm, downwind from the spray source. There was an increase in the number of droplets arriving at the targets when 20% oil was added to the aqueous solution. An even greater increase was seen when oil only was sprayed; these results are compared with sprays containing water and a 5% wetting agent. Droplet size and air turbulence effects are discussed, as is the faster evaporation of water-based sprays. The work was carried out on rhododendron leaves using Saturn yellow fluorescent dye as a tracer using a Micron Mini-ULVA and Ulvapron oil. A comparison is made with the use of Shell oil A and Risella 33 used by pest workers.