is a material added to a pesticide formulation that enhances the performance of the active ingredient. Petroleum oils are commonly used as adjuvants. An adjuvant can improve pesticide effectiveness in a variety of ways, for example by: reducing surface tension, which permits finer droplet size and better surface coverage; reducing volatility, which minimizes evaporation to control spray drift and provide adequate surface residence time; lowering water solubility to resist rain washoff and weathering; and modifying plant or insect surfaces to improve pesticide uptake.

Also see agricultural oil.