The VP candidates discuss the economic bail-out plan
The two US vice-presidential candidates have traded blows on the financial crisis, climate change and foreign policy in their only TV debate.
Democrat Joe Biden sought to link Republican presidential candidate John McCain to the policies of President Bush, saying he was "no maverick".
Republican Sarah Palin defended herself against claims of inexperience and said the McCain ticket would bring change.
Voter polls suggested Mr Biden had won but Mrs Palin did better than expected.
The debate at Washington University in St Louis, Missouri, was seen as particularly crucial for Mrs Palin, whose poll ratings have fallen.
The BBC's Jane O'Brien in Washington says Mrs Palin played to her strengths and her image as a mother in touch with ordinary Americans.
For the most part she spoke fluently but simply about the economy, climate change and the war in Iraq, our correspondent says, and there were few of the stumbling gaffes that have become the staple of late-night comedy shows.
Two polls conducted after the debate, by US networks CNN and CBS News, judged Mr Biden the winner. However, the CNN poll found a large majority thought Mrs Palin had done better than expected.
Asked by moderator Gwen Ifill who was at fault for the current problems with the US banking system, Mrs Palin blamed predatory lenders and "greed and corruption" on Wall Street.
It would be a travesty if we were to quit now in Iraq
Mr Biden pointed to climate change as one of the major points on which the two campaigns differed, saying: "If you don't understand what the cause is, it's virtually impossible to come up with a solution."
He said he and Mr Obama backed "clean-coal" technology and accused Mr McCain of having voted against funding for alternative energy projects and seeing only one solution: "Drill, drill, drill."
While Mrs Palin described her party's candidate as "the consummate maverick", her rival argued that Mr McCain had followed the Bush administration's policies on important issues such as Iraq.
"He's not been a maverick on virtually anything that people talk about around the kitchen table," Mr Biden said.
Overall, commentators highlighted Mrs Palin's frequent use of a "folksy" style, for example using expressions like "doggone it" and telling her opponent: "Aw, say it ain't so, Joe."
They also noted how Mr Biden appeared emotional as he talked about raising his two young sons alone after a car crash killed his first wife.
According to a Pew Research Center poll, two-thirds of voters planned to follow the debate, far more than in 2004.
Sarah Palin was a huge hit at the Republican convention last month
A new poll by the Washington Post suggests that 60% of voters now see Mrs Palin as lacking the experience to be an effective president.
One-third say they are less likely to vote for Senator McCain, as a result.
Independent voters, who are not affiliated to either political party, have the most sceptical views of the 44-year-old Alaska governor.
Another poll, for CBS News, gives Senator Barack Obama 49% to 40% for Mr McCain.
It is the latest in a series of opinion polls that have shown a significant shift in the direction of Mr Obama since the economic crisis began.
Mrs Palin, whose fiery speech at last month's Republican convention inspired Christian conservatives, produces unusually strong feelings - both positive and negative - among voters.
Key words used most frequently by Sarah Palin in the debate
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