The shooting happened at 12:42 a.m. in the 200 block of Potrero Avenue near 19th Street.
Police found 17-year-old San Pablo resident Devaughn Frierson dead on a lawn and a second 17-year-old boy critically injured in the street. He was taken to John Muir Medical Center in Walnut Creek, Gagan said.
The third victim, a 21-year-old man, walked to Kaiser Richmond Medical Center and is expected to survive his injuries.
Initial reports indicated that about 20 shots were fired, but because of the dark and rainy weather, police have so far found few witnesses, Gagan said.
The shooting marks the city's 28th homicide this year, down from 47 last year, Gagan said.
Although it is too early in the investigation to say whether the shooting was gang-related, Gagan said the victims were known to police and that officers are taking steps to try to prevent retaliation.
Anyone with information about the shooting is asked to call Detective Avon Dobie at (510) 231-3053.