The combined sales of South Korea's four credit rating companies fell 0.2 percent on year in 2016, due to a decline in sales of corporate bonds, data showed Tuesday.

Total sales for four credit rating firms -- NICE Investors Service, Korea Investors Service, Korea Ratings and Seoul Credit Rating & Information -- stood at 82.76 billion won ($73.2 million) last year, compared to 82.95 billion won a year earlier, according to the data by the Financial Supervisory Service. 

Last year, sales of corporate debts slipped 28.6 percent on year to 24.4 trillion won, the FSS said.

South Korea's credit rating market is controlled by an oligopoly of three firms -- NICE Investors Service, Korea Investors Service and Korea Ratings, with Seoul Credit Rating & Information only having a very marginal presence.

The market share of NICE Investors Service fell 0.6 percentage point to 34.8 percent last year.

Korea Investors Service saw its market share decline 0.3 percentage point to 32.4 percent last year, while the market share of Korea Ratings rose 0.8 percentage point to 32.4 percent, according to the data. 

The data showed that 46 companies saw their credit ratings rise last year, up 76.9 percent from a year earlier.

The number of companies which faced a downgrade in their credit ratings fell to 91 last year from 159 in 2015, according to the data.(Yonhap)