Visa Inc, the world's largest credit card network, said on Monday it hoped to raise up to $18.8bn (pound 9.6bn) in its long-awaited flotation, which will bring a badly needed financial boost to some of the US's biggest banks.

Visa has decided to press ahead with what will be the largest ever initial public offering in the US in spite of nervous equity markets and the threat of a global economic slowdown.

Michael Lafferty, head of Lafferty Group, a card consultancy, said the decision to go ahead may reflect pressure from its US bank shareholders which include Citigroup, Bank of America and JPMorgan Chase.

"All of these banks suffered heavy writedowns in the wake of subprime mortgage difficulties, and the proceeds from Visa's IPO would go some way to alleviating pressure on their 2008 results."

Ironically, the biggest shareholder, JPMorgan Chase, is one of the financially strongest of the top US banks. It stands to make a total gain of around $4bn, while Bank of America will make about $2bn and Citigroup roughly $1bn. The banks will cash in about half their stakes in the IPO. JPMorgan and Goldman Sachs are the lead underwriters of the issue.

Visa's IPO, which is expected in March or April, comes two years after the flotation of Mastercard, its smaller rival which was also owned by its bank members. The shares have soared by more than 400 per cent.

Both networks, which process transactions for the banks that issue their cards, have been helped by strong global economic growth and rising international travel.

They are also seeing a rapid switch from cash to card usage in fast-growing emerging markets.

The company to be floated combines all Visa's operations outside Europe. Visa Europe is to remain separately owned by its European member banks, which its board says will leave it better positioned to deliver a borderless payment market in line with the European Commission's vision of a Single Euro Payments Area.

According to Lafferty Group, the markets in which Visa Inc operates showed annual growth of billed volumes of 24.6 per cent over the past two years compared with 9 per cent in Europe.

Mastercard's shares have continued to perform strongly in recent months in contrast to credit card issuers, such as American Express, which are exposed to rising bad debts.