Lane Florsheim writes in The New Republic writes Death Penalty Evolution Map: How Executions Have Changed in States "By 2009, all death-penalty states had made lethal injection the sole or primary execution method for death row inmates, despite problems with the method that have been evident since the 1950s. Now, the death penalty is transforming once again, due to a shortage in the drug used in the three-drug protocol to paralyze the inmate during his execution. As a result, states have resorted to hunting for a replacement in unusual places, such as domestic compounding pharmacies. Some have changed their protocols to use just one drug, or tried to replace the missing drug with new drugs. Others have put executions on hold. In states such as Louisiana, Tennessee, and Wyoming, there’s even been talk of reintroducing the electric chair. This has led to a spate of ethical problems and legal challenges."
Sadly the animation in the above map doesn't seem to be playing in my copy, click to visit the page to see the changes over time.