Are gas chambers still used today?

There are three states that still use the gas chamber as their method of execution. They are Arizona, Missouri and Wyoming. In Arizona a person sentenced to death after November 15, 1992 can elect gas over injection. In Missouri gas or injection may be used. In Wyoming gas is used if injection is deemed unconstitutional. The last time gas was used was in 2010 during the execution of Walter LaGrand in Arizona.