Companies from all sectors of the credit markets came to market with bond offerings Wednesday, including a $4.5 billion deal from lender GMAC LLC that benefited from government backing.

Rates in the corporate debt markets are at multiyear lows, allowing a multitude of companies to raise cheap funding from investors eager for returns that on average are double those available on government debt.

U.S. dollar-denominated, investment-grade supply totaled $113.4 billion in May, according to Dealogic, and given the current market environment, June could top that. In the first two days alone, $3.8 billion in new offerings were sold, according to Dealogic.

"The buying frenzy continues unabated," said Tom Murphy, sector leader and portfolio manager at RiverSource Investments. "We have heard June's calendar is going to be huge....The market is open to anyone."

The difference in risk premiums between a newly sold issue and an outstanding one from the same or a comparable company, known as the concession, has drastically narrowed over the past several months as investors have also been snapping up corporate debt in the secondary market.

Wednesday's docket included billion-dollar deals from U.K. telecoms group Vodafone PLC (VOD) and U.S. insurer MetLife Inc. (MET), as well as a $1 billion dollar offering from Brazil's development bank BNDES which yielded 6.546%.

GMAC LLC, the auto lender affiliated with bankrupt auto giant General Motors Corp. (GMGMQ) sold its first government-guaranteed note Wednesday.

The $4.5 billion offering was split into a $3.5 billion three-year fixed rate part, which yielded 2.247%, or 0.80 percentage point over Treasurys. The $1 billion three-year floating rate part was sold with a yield equivalent to three-month Libor, a benchmark rate for short-term lending. Three-month Libor was fixed Wednesday at 0.63688%.

Junk-rated GMAC converted to a bank holding company late last year and received permission from regulators to issue up to $7.4 billion in debt on May 21. Currently, GMAC's unsecured debt is rated C by Moody's Investors Service and CCC by Standard & Poor's.

The sale of FDIC-backed debt and access to the FDIC's program is crucial to the company's survival, said James Lee, senior fixed-income analyst at Calvert Asset Management Co. "Otherwise, they would have to tap the market with bonds that yield 11% to 12% and have a large interest expense burden," he said.

Banc of America Securities LLC, Barclays, Deutsche Bank and JP Morgan underwrote the issue.

Risk premiums on FDIC-backed debt have ratcheted in since the program began.

When Goldman Sachs (GS) sold the first issue via the FDIC program in November 2008, the 3.5-year note was priced at a risk premium of 2.00 percentage points over Treasurys. That issue was bid at 0.39 point over Treasurys, according to Tradeweb, an electronic trading platform.

-By Kellie Geressy and Andrew Edwards; Dow Jones Newswires; 201-938-2050; kellie.geressy@dowjones.com

(Kate Haywood contributed to this report.)