Florida topped a 35-state study by increasing the average time prisoners spent behind bars by 166 percent from 1990 through 2009.
The study released Wednesday by the Pew Center on the States says that increase resulted in Florida spending an extra $1.4 billion on prisons in 2009.
One key factor in lengthening Florida prison stays was a 1995 law that requires inmates to serve at least 85 percent of their sentenced before release.
Another was tougher penalties. That includes Florida's 10-20-Life law that sets minimum mandatory sentences for crimes committed with firearms.
A companion analysis found some nonviolent prisoners could have been released up to two years earlier with little or no effect on public safety, saving the state millions.