Commercial banks added nearly $30 billion of mortgage-backed securities to their portfolios dur-ing the second quarter, but the industry’s stake isn’t getting any bigger in the MBS market. Commercial banks held a record $969.77 billion of MBS in their portfolios as of the end of June. That represented a tidy 3.2 percent gain from the previous quarter, and it was up a solid 8.1 percent from the same point in 2005. But commercial bank holdings of mortgage securities accounted for an estimated 17.6 percent of total... [Includes three charts.]