In Fiscal Year 2015, according to the US Sentencing Commission:
"In 22.2% of all cases, the offender was convicted of an offense carrying a mandatory minimum penalty.
"• Drug trafficking offenses accounted for over two-thirds (66.2%) of the offenses carrying a mandatory minimum penalty, followed by firearms (15.4%) and child pornography offenses (8.8%).
"• Almost 40 percent (39.2%) of offenders convicted of an offense carrying a mandatory minimum were relieved of the mandatory minimum penalty because:
"•• 20.3% received relief solely by providing the government with substantial assistance;2
"•• 13.0% received relief solely through the statutory safety valve provision,3 and
"•• 5.8% received relief through both the statutory safety valve provision and by providing substantial assistance to the government.
"• After relief was applied, 60.8% of these offenders remained subject to a mandatory minimum penalty at sentencing, reflecting 13.5% of all federal offenders."

Source

US Sentencing Commission, Quick Facts on Mandatory Minimum Penalties, May 2016.
http://www.ussc.gov/research/…
http://www.ussc.gov/sites/def…