Law enforcement officials in Alameda County said 23 percent of businesses targeted in a Thursday sting sold alcohol to minors.
The operation, conducted by the Alameda County Vice Enforcement Team, targeted 119 establishments and found 28 businesses sold an alcoholic beverage to a "decoy" under 21 years old.
During the operation, law enforcement agencies sent a person under 21 years old into businesses to try and buy alcoholic beverages, according to law enforcement officials.
The "decoy" is truthful about his or her age and provides a true identification card if asked.
Law enforcement officials said the goal of the operation is to ensure businesses are making appropriate and legal efforts to prevent the sale of alcoholic beverages to underage people.
Five teams conducted the operation throughout Alameda County in Hayward, Alameda, San Leandro, Emeryville, Albany, Union City, Pleasanton, Livermore, Newark and Castro Valley.
The state average buy rate during this type of operation is 18 to 22 percent, officials said.