In its study, comScore said that during the third quarter of 2008, four out of the top five US banking websites saw customers spend less minutes on their site per visit compared to a year ago.
The company said this could make it significantly more difficult for banks' marketers to reach potential and existing customers at a time when many institutions are desperate to recruit new account holders.
Figures from the study show that in the third quarter of 2007, the top three online banking sites accounted for 60 per cent of the top ten's customers. Following recent mergers and acquisitions brought on by the credit crisis, they now account for 80 per cent.
In this environment, many of the larger banks have launched "aggressive customer-acquisition campaigns" to further consolidate their position.
Marc Trudeau, senior director of financial services at comScore said: "In this time of uncertainty and change in the industry, many of these firms, regardless of their marketing strategies or business objectives, are turning to the internet."
Founded in 1999, comScore is a digital market intelligence specialist whose clients include the Financial Times, Deutsche Bank and the BBC.