Corporate bond issuers face having to roll over a record amount of debt in the coming years amid declining investor risk appetite and falling credit quality, the OECD said on Monday.

Non-financial companies will have to pay back or raise fresh debt worth more than $4 trillion in the next three years, the Organisation for Economic Cooperation and Development said.

To put that into perspective, it was close to the balance sheet of the United States Federal Reserve, the Paris-based policy forum said.

Despite a drop in net issuance last year, a decade of companies gorging on debt amid record low interest rates in many countries has pushed the amount of debt on companies' books to record levels.

As of the end of last year, global outstanding corporate debt issued by non-financial companies stood at $13 trillion, the OECD said.

That's even after net issuance dropped 41 percent last year to the lowest volume since 2008, which was just as the global financial crisis was getting under way.

"Importantly, net issuance of non investment grade bonds turned negative in 2018, indicating a reduced risk appetite among investors," the report said. "The only other year that this happened over the last two decades was in 2008."

Rating's agency Standard & Poor's said earlier this month that issuance was facing headwinds from rising interest rates in the United States and Europe, uncertainty around Brexit and slower growth in China and many developed countries.

While companies have grown increasingly dependent on debt over the last decade, the quality of the bonds they have issued has broadly fallen.

The share of bonds rated BBB - the last rung on the ratings scale before junk status - stood at nearly 54 percent, the highest in records going back to 1980, the OECD said.

Against that background, corporate bond issuers in advanced and emerging countries are facing the highest repayments since 2000 in the coming three years, the OECD estimated.

"In a rising rate environment, when issuers' refinancing needs arise, borrowing costs will inevitably increase," the report said.