The company, which sells real-time news and data to financial markets, said that its own research had found its revenue share of the £6bn global financial information market had fallen two points from 39% in 2002 to 37% in 2003.
In a statement, the company said that it gained against its biggest rival Bloomberg at the "premium" end of the market in 2003.
Chief executive Tom Glocer said: "The drop in overall market share is not unexpected and I am confident that the strength of our new products in the mid-tier and our investment in service will be the basis for strengthening our overall position."
Last month it was announced that Niall FitzGerald, regularly cited as the most powerful marketer in the UK, is to succeed Sir Christopher Hogg as chairman of Reuters in October. FitzGerald will take up the post when he steps down as chairman and chief executive of FMCG giant Unilever.
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