The Globe and Mail reports in its Saturday edition if you choose an all-bank stock portfolio, be aware of the risks. The Globe's John Heinzl writes Canadian banks have a unique advantage in that they basically operate an oligopoly, where a small number of players dominate the market. Because of their scale, they have been able expand into investment banking, wealth management and insurance. Their steady growth has allowed them to post rising earnings and announce regular dividend increases. Customers may not always love them, but Canadian banks have performed exceptionally well for investors. For the five years ended Sept. 30, the average annualized total return was 12.8 per cent for the Big Five. That easily topped the S&P/TSX composite index's total annualized return of 8.6 per cent. The banks came out well ahead over longer holding periods as well. Canadian banks may be strong and well-regulated, but the 2008-09 financial crisis showed that banks can fail. If they can fail in the United States they can fail here, too. Even some large U.S. banks that were bailed out by the government are still well below their precrisis levels. Citigroup, for example, trades at less than one-10th of its former high.