With a visual picture much closer to cruise than normal takeoff attitude, we managed to clear the semi with room to spare and were on our way. Our direct route to Santa Rosa would take us through San Francisco’s Class B airspace. In the dozens of trips I’ve made over the city, I’ve never been denied the Bravo transition, and had no reason to suspect anything different this time. Which is why I planned a flight with just 24 gallons of fuel on board — light enough to take off with just enough for the two-hour flight, a moderate headwind and a double-than-legal one-hour reserve. When the NorCal approach controller failed to utter the magic words “cleared into Bravo” and handed us off, we were already under the Class B shelf. When the next controller abruptly advised us to remain outside Bravo, my fuel calculations predicated on direct routing were suddenly invalid. We turned northward, dropped down to 4,500 feet to remain below the approaching layer of the upside-down wedding cake and added a good 10 minutes to our route as we flew just outside the Class B perimeter.