International urged a moratorium on rising executions in the conservative kingdom.
The executions brought to 127 the number this year in Saudi Arabia, compared with 87 in 2014, according to AFP tallies compiled from interior ministry statements.
Saudi Nawaf al-Otaibi was executed in the western city of Taif after being convicted of shooting dead his father in a dispute, the interior ministry said.
Fellow Saudis Bandar al-Ghathim and Abdulaziz Mohammed al-Zahrani were executed in the country's southwest for murder, the ministry said in statements carried by state news agency SPA.
Syrian Ezzeddine al-Saleh was executed in the northern Jawf region for trafficking in amphetamines, the ministry said.Under Saudi Arabia's strict legal practices, murder, armed robbery, rape, drug trafficking and apostasy are all punishable by death.
Most people sentenced to death in Saudi Arabia are beheaded, but sometimes firing squads are used.
Amnesty International on Tuesday criticised Saudi Arabia's "deeply flawed judicial system" as it issued a new report on the rising number of executions.
The London-based group criticised trials it said "blatantly flout international standards", citing secret hearings, denying defendants access to lawyers and convictions based on confessions "obtained under torture".
"Saudi Arabia's sharia (Islamic) law-based justice system lacks a criminal code, leaving definitions of crimes and punishments vague and widely open to interpretation," Amnesty said.
Amnesty says Saudi Arabia is one of the world's most prolific executioners, along with China, Iran, Iraq and the United States.