Douglas Flint, chairman of HSBC Holdings Plc, wants to know who's going to buy the trillions of dollars of loss-absorbing securities that regulators plan to force the biggest global banks to have on their books.

The interest at this stage from traditional consumers of bank paper, such as pension funds and insurers, is lukewarm at best. While the securities, designed to be written down in a crisis, would offer higher yields than senior debt, the risk of bail-in may be more than some buyers can tolerate. That could leave the banks struggling to meet regulatory requirements.

"We're accustomed to fixed-income instruments that are relatively 'sleep-at-night' securities and which have a recovery value if things go wrong," said Alex Thompson, a principal in the fixed-income manager research team at pension-fund adviser Mercer in London. "This type of financial debt has a risk-reward profile that's not really appropriate for a pension fund's fixed-income portfolio."