Oil adjuvants can reduce rainfast periods, provide more uniform droplet size, and result in less spray evaporation and provide excellent penetration of herbicide into waxy leaves. Examples are Emulsified Petroleum-based Oils (Crop Oils and Crop Oil Concentrates), and Methylated Seed Oils (occasionally referred to as Methyl Esters or MSO). The most common examples of oil adjuvants are:
- Methylated seed oils: Occasionally referred to as methyl esters. The products in this group are specific in their adjuvant effect. They function exceptionally well with many herbicide chemistries. Vegetable seed oils all contain constituents called fatty acids. These organic acids may be transformed by a process called esterification by reacting with an alcohol. In methyl ester production, the fatty acids are esterified with methyl alcohol. The end result is a seed oil with new properties of solvency and water affinity.
- Emulsified petroleum based oils: Commonly called crop oil concentrates or oil surfactants. The usual ratio is 16 to 20% surfactant emulsifier and 80 to 84% petroleum based oil.