Global banks have disclosed 80 per cent of forecast losses on subprime mortgage-related assets, meaning further ratings actions due to losses on these instruments are likely to be "minimal," Fitch Ratings said on Wednesday.
Fitch forecasts total losses for the $1.4 trillion subprime mortgage market of around $400 billion, of which 50 per cent reside within the banking sector and the remainder among financial guarantors, insurers, asset managers and hedge funds.
It said banks had announced losses of $165 billion already on exposures to residential mortgage-backed securities (RMBS) or collateralised debt obligations backed by asset-backed securities (CDOs of ABS).
"As a significant proportion of the losses have been disclosed, further ratings action arising from ABS-CDO and subprime RMBS exposures is likely to be minimal," the ratings agency said in a report.
Fitch said estimates based on market prices of indexes such as the ABX and TABX indexes, based on subprime securities, showed that losses could be as high as $550 billion.
However it said such indexes were "at best an imperfect proxy" for valuations, with prices reflecting a host of non-credit-related factors, and that actual losses would be in line with its $400 billion forecast.
Losses on some types of instrument are set to be steep. For securities originated in 2007, just before the credit crisis hit, Fitch estimates losses on RMBS could be as high as 26 per cent, on CDOs of high-grade ABS around 60 per cent, and on CDOs of mezzanine ABS around 85 per cent.
Credit ratings agencies have come under fire for assigning high ratings to these securities and then downgrading them sharply after the structures that were supposed to protect investors from losses proved flawed.
Fitch estimates that losses disclosed to date are evenly split between Europe and the United States, with $77 billion of losses racked up by each. Asia has seen just $10 billion of losses, the agency said.
However, the agency noted just four banks -- Citigroup, Merrill Lynch, UBS and IKB --had accounted for around 60 per cent of disclosed losses.