Korea's three major energy-related public companies are to pay back more than 8 trillion won ($6.8 billion) in debts maturing this year, which stemmed from their heavily leveraged investments in overseas energy assets, government data showed Tuesday.

The Korea National Oil Corp. (KNOC), the Korea Gas Corp. (KOGAS) and the Korea Resources Corp. (KORES) carry a collective maturing debt of 8.29 trillion won to be paid back by the end of 2016, according to the All Public Information In-One (ALIO).

"To settle our short-term debts maturing this year, we are planning to raise funds by issuing bonds or using our own cash reserves. In addition, we will ask the lenders to roll over the maturity date of short-term loans," KNOC spokesman Cho Jeong-geun said. 

KOGAS and KORES said on Tuesday they will also take similar steps to repay their short-term debts that should be paid back within this year.

At the end of December last year, KOGAS carried a short-term debt worth 3.96 trillion won, followed by the KNOC with 3.34 trillion won and KORES with 985.6 billion won. When their long-term debts were factored in, the three utilities' combined debts reached a whopping 46.589 trillion won, ALIO said.

In contrast, their cash and cash equivalents totaled 642.1 billion won, the government data services showed.

"Despite their fundraising plans and expected government subsidies, the companies will have some difficulty in regaining a clean bill of health for some time due to the unfriendly business environment," an industry official said.

The state-run utilities heavily borrowed from financial institutions during the Lee Myung-bak administration that ended in February 2013 to invest in overseas oil and gas fields to reduce the country's heavy dependence on overseas energy assets.

In many cases, however, they have failed to even retrieve their investment money, let alone investment gains.

KNOC was the biggest loser. Its net losses deepened to 4.5 trillion won in 2015 from 1.61 trillion won a year earlier as the value of the oil and gas fields they invested in fell sharply due to low oil prices.

KOGAS posted a 29 percent on-year decline in net profit at 319.19 billion won last year. KORES, an unlisted company, saw its net losses widen to 2.06 trillion won from 86.51 billion won. (Yonhap)