"Nerve agents are the most toxic of the known chemical warfare agents. They are chemically similar to organophosphate pesticides and exert their biological effects by inhibiting acetylcholinesterase enzymes. G-type agents are clear, colorless, and tasteless liquids that are miscible in water and most organic solvents. GB [Sarin] is odorless and is the most volatile nerve agent; however, it evaporates at about the same rate as water. GA [Tabun] has a slightly fruity odor, and GD [Soman] has a slight camphor-like odor. VX is a clear, amber-colored, odorless, oily liquid. It is miscible with water and soluble in all solvents. It is the least volatile nerve agent."
U.S. Department of Health and Human Sevices: http://www.hhs.gov/gulfoilspill/
Managing Hazardous Materials Incidents, Volume 3