Gas boycotts -- Why not have everyone buy only gas from ONE company?

Of course, their profits would skyrocket but Exxon, Chevron etc. would bottom out at the same time. Say if, for instance, Americans agreed to only purchase gas from a BP station that would be 'do-able' for any of us. To boycott say Exxon is harder to do because I don't know which other 'name-brands' that they own.