American depositary receipts - securities used by firms to attract US investment - add as much as 10 per cent to a company's share price in the first year of issue, according to new research.

Oxford Metrica, the financial consultancy, says a subsequent upgrade from a depositary receipt traded over the counter to one with a full US listing adds on average a further 15 per cent to a share price.

The rise is caused by the value US investors put on the additional financial disclosure required by the Securities and Exchange Commission and the US's generally accepted accounting principles, or GAAP. Oxford Metrica's research is sponsored by the Bank of New York, one of the biggest arrangers of American depositary receipts, the most important category of these assets.

The research is released at a time when those with involvement in ADRs have been feeling the pressure from the Sarbanes-Oxley Act, passed last year.

Firms such as Daiwa of Japan, Porsche of Germany and Benfield Group of the UK have cited the Act as a reason for not listing ADRs on US exchanges. In April the SEC relaxed some of the Act's rules after issuers said there were conflicts with legislation in their home countries.

In addition, many European firms have been reassessing the value of their secondary listings during the downturn. Swedish telecoms equipment maker Ericsson last year cut its number of listings from six to three.

ADRs meet the needs of US domestic fund managers, many of whom can only invest in dollar-denominated assets for legal and regulatory reasons. There are also global depositary receipts, which can be listed on any exchange including New York's. ADRs on the London Stock Exchange tend to be issued by Asian and emerging market firms. The Oxford Metrica research showed that a listed depositary receipt improved liquidity by 32 per cent on average as the stock's visibility rose.