; of these, almost 250,000 (61 percent) received mandatory minimum sentences. (7) According to the U.S. Sentencing Commission, drug offenders released from prison in 1986 who had been sentenced before the adoption of mandatory sentences and sentencing guidelines had served an average of 22 months in prison. In 2010, almost two-thirds of all drug offenders received a mandatory sentence, with most receiving a 10-year minimum. Most of these offenders are nonviolent or lower-level offenders with little or no criminal history: in 2010, 51.6 percent had few or no prior convictions, 83.6 percent did not have weapons involved in their offense, and only 6 percent were considered leaders, managers, or supervisors of drug operations. (8) Mandatory minimum sentences have consistently been shown to have a disproportionate impact on African-Americans. The United States Sentencing Commission, in a 15-year overview of the Federal sentencing system, concluded that mandatory penalty statutes are used inconsistently and disproportionately affect African-American defendants. African-American drug defendants are 20 percent more likely to be sentenced to prison than White drug defendants. (9) According to the U.S. Sentencing Commission, between 1994 and 2003, the average time served by African-Americans for a drug offense increased by 62 percent, compared to a 17 percent increase among White drug defendants. (10) According to the Substance Abuse and Mental Health Services Administration, government surveys document that drug use is roughly consistent across racial and ethnic groups. While there is less data available regarding drug sellers, research from the Office of National Drug Control Policy and the National Institute of Justice has found that drug users generally buy drugs from someone of their own racial or ethnic background. But, according to the U.S. Sentencing Commission, over 70 percent of all Federal narcotics offenders sentenced each year are African-Americans and Hispanic Americans, many of whom are low-level offenders.