Police responded to a report of shots fired in the 5600 block of Main Street at 1:41 a.m., police said.
Officers arrived at the scene and found a man suffering from three to four gunshot wounds, police said.
The 28-year-old man, whose name was not released, was transported to a hospital where he was pronounced dead, according to police.
There are no details of why or how the shooting happened, and there are no leads on any suspects, police said.
Police, along with the sheriff's office, are still investigating.
Anyone with information about the shooting is asked to call Oakley police at (925) 626-2411.