Small Aircraft; Low Wing; 1 Eng; Retractable Gear
Flight Crew Commercial; Flight Crew Instrument
Flight Crew Last 90 Days 3; Flight Crew Total 487; Flight Crew Type 155
ATC Issue All Types; Conflict NMAC
General None Reported / Taken
Procedure
I was coming back from ZZZ on an Oakland transition through Class Charlie airspace. I was given an instruction to fly from Coliseum to the 30 numbers of OAK at 2000 feet as instructed. I passed over the coliseum and turned right to 30. Right before the handoff from north tower to south tower - an aircraft came direct head on at my 12 o'clock - passed underneath me way too close. Probably 100-200 feet. Scared the [expletive] out of me. I was never given a traffic advisory or any info about this aircraft; even though I was in the middle of the OAK tower airspace pretty much right over the parallel runways. My guess is they were transitioning to the east; probably talking to the south tower - but they didn't give the north tower the memo. Very disconcerting. ADS-B wasn't too helpful there because I was right over the airport and there were a lot of targets (on ground and in air) - so it was hard to make any sense of traffic scope with the targets overlapping. I was about notify tower of the close encounter; but was then given another target at my 12 o'clock; but this time ahead of me and headed in the same direction over the Bay. I focused on flying the airplane; and [continued to my destination] safely.
GA pilot reported NMAC with unreported traffic on transition through Class C airspace.