De Beers will also disclose no let-up in the problems affecting the industry, which also threaten its own dominance, a position it has enjoyed since the 1930s.
The CSO figures, due on Wednesday, will show that sales fell from dollars 3.93bn (pounds 2.6bn) in 1991 to about dollars 3.25bn last year. This will mark the second annual decline and analysts are expecting De Beers to add to the gloom with a bearish forecast for this year, predicting only a marginal recovery in fortunes.
De Beers has already had to impose a 25 per cent cut in production on diamond producers selling through the CSO, and has indicated it might make a dividend cut for only the second time in its history.
The company's woes have been compounded by illicit diamond mining in Angola and the failure of Russia and Sakha, the new independent republic in former Siberia, to finalise a new supply deal with the CSO.
The main problem, though, has been a fall in world demand. The recession has gradually hit the CSO's main markets with the downturn in Japan and a sharp destocking by Japanese jewellers bringing about the latest collapse.
Steve Oke, mining analyst at Smith New Court, says the Japanese market is still declining. The only ray of hope is from the US, although recovery there is still weak.
In Angola, renewed fighting in the long-running civil war is good news for De Beers. Last year, about pounds 500m of diamonds were illegally mined during lulls in the fighting - twice the official production of the country.
Mining has since stopped during the outbreak of war, but any pause could mean that Angolan gems will start flooding back onto the market.
Russia is also uncertain. The parliament has yet to fully ratify a new agreement under which the CSO will sell all Russian and Sakhan diamonds until 1995. The Russians also want to set up as many as 15 new diamond-cutting centres which could bring down the price of cut gems.
Reports from Antwerp, one of the main diamond cutting centres, indicate a still subtantial flow of diamonds coming from Russia and not being sold through the CSO.