The shooting ignited petrol and diesel drums and triggered a massive fire.
Eight women and three children were among the dead. A woman with serious injuries was taken to the port city of Karachi for treatment.
Seven of the bodies were beyond recognition, they said.
The petrol pump was engulfed by the fire and several employees were killed.
Five shops, a rickshaw and a motorcycle were gutted while some shops were damaged.
No group claimed responsibility for the attack.
Balochistan has been rocked by widespread sectarian and ethnic violence over the past few years.