First billion-dollar election

Fundraising:The 2008 presidential election is almost a year away, but it is already on course to be the most expensive in US history and could be America's first billion- dollar election. During the first nine months of 2007, the Republican and Democratic candidates raised a total of $420 million, with Democrats out-raising Republicans by a wide margin.

Hillary Clinton and Barack Obama have had the most spectacular success, netting $91 million and $80 million respectively by the end of September.

On the Republican side, former Massachusetts governor and multi-millionaire Mitt Romney leads the pack with $63 million, $17 million of which came from his own pocket. Rudy Giuliani took in $47 million and John McCain raised $32 million - although he spent nearly all of it on a bloated campaign staff early in the year, many now sacked.

Candidates need money to produce ads and buy airtime, run offices in key states and pay staff, who organise events, man phone banks, knock on doors and raise more money. Each American citizen or Green Card holder can give a candidate up to $2,300 for the primary campaign and a further $2,300 for the general election. Any contributions raised for the general election must be returned if the candidate fails to win the party's nomination.

Political action committees which support more than one candidate can give up to $5,000 to each presidential candidate and other political committees can give up to $2,300 to each candidate.

These limits make traditional fundraising laborious for candidates, even if rich supporters continue to "bundle" donations from numerous individuals. The internet has proven to be a cheap and efficient fundraising tool, allowing Obama almost to match Clinton in funds raised.

Obama has a further advantage as the campaign progresses because most of his donors have given relatively small sums, whereas Clinton has relied on fewer donors, many of whom have already given the maximum contribution allowed.

Obama can raise money more quickly by returning to his large donor base again and again, asking for further contributions of $100 or $200 a time.

Most of the main candidates have refused federal matching funds, which set limits on the amount they can raise, and some campaign experts predict that each party's nominee may have to raise $500 million by the time America votes next November.