Central bankers hinting at more monetary stimulus have depressedyields so much that even some European junk bonds are trading atlevels where investors have to pay for the privilege of holdingthem.

The number of euro-denominated junk bonds trading with anegative yield—a status until recently associated only withultra-safe sovereign borrowers—now stands at 14, according to datacompiled by Bloomberg. At the start of the year there werenone.

Cheap-money policies since the financial crisis have keptinterest rates for the past decade at, or near, all-time lows.That's prompted many investors to buy riskier assets that yieldenough for them to meet their liabilities, driving bond marketshigher and yields lower. The European Central Bank (ECB) said onMonday it's ready to add more stimulus to the Eurozone, indicatingthat an end to the age of ultra-low borrowing costs is far fromover.