All eight were sentenced under old federal guidelines that treated convictions for crack cocaine offences harsher than those involving the powder form of the drug. Obama also pardoned 13 others for various crimes.
The president signed the Fair Sentencing Act in 2010 to cut penalties for crack cocaine offences in order to reduce the disparity. But the act addressed only new cases, not old ones.
Obama said those whose sentences he commuted yesterday have served at least 15 years in prison, many under mandatory minimums that required judges to impose long sentences even if they didn't think the time fit the crime.
In the previous five years of his presidency, Obama had only commuted one drug sentence and pardoned 39 people. A pardon forgives a crime and wipes out the conviction, typically after the sentence has been served. A commutation leaves the conviction but ends the punishment.
White House officials say Obama had only approved a single clemency petition among more than 8,000 received because it's the only one that had been given a positive recommendation by the Justice Department.
The old sentencing guidelines subjected tens of thousands of blacks to long prison terms for crack cocaine convictions while giving far more lenient sentences to those caught with powder who were more likely to be white. It was enacted in 1986 when crack cocaine use was rampant and considered a particularly violent drug.
