Last year, President Barack Obama signed legislation that reduced the federal sentencing disparity between the two types of cocaine from 100-to-1 to 18-to-1.
Before Obama signed the Fair Sentencing Act, someone caught with 5 grams of crack cocaine had received the same sentence as someone caught with 500 grams of powder cocaine.
Thirteen states have sentencing laws that treat the drugs differently.
Only two - Missouri at 75-to-1 and New Hampshire at 28-to-1 - have ratios higher than the U.S. government's.
The Washington-based Sentencing Project on Thursday urged states
to get rid of the disparities, citing fairness and potential savings in prison budgets.