After the 1990-1991 Gulf War, Iraq reported to the UN a chemical weapons stockpile that included: 75 tons of Sarin, 500 tons of Tabun, 280 tons of mustard gas, and 30 chemical weapon warheads for Scud and al-Hussein missiles. Saddam’s regime had used chemical weapons extensively during the 1980’s, both in combat against Iranian forces and against Kurdish civilians in northern Iraq, but they were not used during the 1990-1991 war. Several strategic considerations contributed to Saddam refraining from using chemical weapons during that conflict:
Chemical weapons served as a means to deter Israeli use of nuclear weapons- a scenario which, although highly unlikely, nonetheless loomed large in the minds of Iraqi decision-makers. Saddam knew that Israeli use of nuclear weapons, or threats thereof, were less likely if the Israelis believed he might respond in kind with nerve agents (a response which could, in the right circumstances, inflict significant casualties).
Chemical weapons served as Saddam’s trump card against any potential US-led attempt to push all the way to Baghdad to depose him. Indeed, the WMD threat was part (albeit a comparatively small part) of the decision not to continue on toward Baghdad for the purpose of regime change.
Saddam was well aware that using chemical weapons against Western forces would be a major point-of-no-return that would likely endanger the survival of his regime. Rather than take such a risk, he opted instead to maintain them as his ace-in-the-hole. Saddam himself confirmed this during his interrogations following his capture in 2003.
Coalition military dominance left Iraq with limited means to actually employ chemical weapons. US-led forces, believing that the employment of chemical weapons was at least reasonably likely, largely neutralized Iraq’s artillery and air capabilities, which represent the most effective means of employing chemical weapons for tactical (battlefield) purposes. This left the Iraqis with limited means to use such weapons on the battlefield, at least with any hope of achieving significant effect. Coalition forces had a much harder time, however, neutralizing the Scud missile threat. This left the strategic employment of chemicals via ballistic missiles against neighboring countries as the only means Saddam had of actually inflicting significant casualties with chemical weapons (Iraq’s Scud capabilities were adequate for hitting cities but of limited use against fast moving enemy forces).