The bond market is so hot that some bankers are betting people will snap up 100-year bonds.

These ultra-long-term bonds are risky because the investor must believe that the companies issuing them will still exist in 100 years, according to The Wall Street Journal. But they're attractive because companies pay investors a premium for them.

"Such bonds won't pay off their principal until 2110, a date so far that the people doing today's buying and selling will all be dead," writes Katy Burne.

The big question mark for these bonds are interest rates. No one has a clue what direction interest rates will take over the next century, and they could rise to a point where they outshine any "century bond" return.

But that isn't stopping some bankers from pitching the idea.

"With credit spreads rallying, it's the perfect environment for issuers to get away with 100-year bonds," one banker told the Journal. "There is a natural trend to go long, so the obvious extension of that is to move past the 30-year bucket."

Companies that have sold century bonds in the past include Walt Disney (DIS), Coca-Cola (KO) and transportation companies Norfolk Southern (NSC) and Burlington Northern Santa Fe. Coupons on these bonds are usually in the 7% to 8% range, Burne writes.