Despite having more than 700 inmates on death row, many end up dying of natural causes. Only 13 executions have been performed since voters reinstated the death penalty in 1978.
Since then, the state doled out more than $4 billion for death row. The study predicts those costs will balloon to $9 billion by 2030 when there will be more than 1,000 inmates added.
"The report really points at the Legislature and says you botched it," said Prof. Laurie Levenson of Loyola Law School. "You didn't make the reforms that you would need to have an operative death penalty."
In addition to incarceration costs, sometimes the process of decades-long appeals drives expenses up.
Executions have been on hold since 2006 because of the legal challenge to the use of lethal injection.
Opponents say the study raises questions over whether California should continue to have the death penalty given the state's budget crisis.
"It's a hideous waste of California taxpayers' money," said Mike Farrell of Death Penalty Focus, a non-profit organization dedicated to the abolition of capital punishment. "What we can do and what we should do is eliminate the death penalty entirely."
Because voters brought back capital punishment, they will have to be the ones that have to change or undo it.
"Until the people say that's a penalty we don't want anymore or it costs too much, we can't do it here in California, then we have to keep it," said Assm. Steve Knight (R-Palmdale).
The study's authors say voters were duped at the ballot box and weren't aware of the costs associated with death row. They suggest it's time to put the question back before Californians.