The sharp rise in financial stocks suggests investors believe big banks are done raising large amounts of fresh capital to strengthen their balance sheets. But international bank regulators, with the blessing of national overseers, are readying rule changes that could further increase the amount of capital banks hold, especially in their trading operations.

In recent weeks, Wall Street analysts have started to guess what this extra capital burden could be - and the numbers are surprisingly large. This should give bank investors pause: The stocks are a good buy if the economy continues to recover, but, if reforms are tough, shareholders could face yet more dilution.