The European debt crisis is rocking the global stock markets, many debt markets as well as the Euro.

But one market that seems to be immune from the growing volatility is the market for riskier US corporate bonds.

According to Bloomberg, unsecured bonds are accounting for a growing portion of global debt sales.

So far this year, companies have sold $246.9 billion of unsecured high-yield debt. This works out to 72.6 percent of all junk bond issuance, according to Bloomberg.

This is nearly 150 percent greater than the $112.1 billion sold during the same period in 2009, which accounted for just 61.5 percent of junk bond offerings.

Of course, bond investors' complacence is corporations' gain.

But, why aren't investors becoming more cautious? Liquidity. The US Federal Reserve and its global counterparts are purposely keeping interest rates as close to zero as possible to stimulate the economy. Meanwhile, the Fed is also plunking down $600 billion to buy Treasuries, further adding cash to the system.

"There's so much cash chasing investment opportunities out there that buyers are willing to sacrifice covenants and security," Guy LeBas, chief fixed-income strategist and economist at Janney Montgomery Scott LLC, tells Bloomberg. "We're trying to dodge these covenant-light and low-security deals right now, even though they're popular."

The wire service points out that General Electric issued the largest unsecured dollar bond this half when it sold $2.15 billion of 1.875 percent, three- year notes in September.

The trend among unsecured bonds is especially surprising given that total global corporate bond sales fell 64 percent last week to $30.1 billion, according to Bloomberg.

Although investors may wind up regretting taking on added risk, issuing unsecured debt could prove to be a shrewd cash management decision for below investment grade credits.

Many of these companies that have not recently issued debt may look back to these days of historically low rates and loose covenants as a once-in-a-lifetime missed opportunity.