The US presidential election will be decided in about a dozen battleground states where most opinion polls show Democrat Barack Obama ahead of Republican rival John McCain.
Mr Obama, who leads in every national opinion poll, also led McCain in five of eight key battleground states on the day of the election, according to a series of Reuters/Zogby polls released today.
In two of the most closely watched contests, the Democrat held a 1-point lead in Florida and 2-point edge in Ohio, both within the poll's margin of error of 4.1 percentage points.
Mr Obama had bigger leads in Virginia, Nevada and Pennsylvania, while Mr McCain was ahead in Indiana and North Carolina, the Reuters/Zogby poll showed. Missouri, a classic bellwether state, was dead even.
The victor needs 270 electoral votes to win the Electoral College and capture the White House
The president is determined not by the most votes nationally but by a majority of the Electoral College, which has 538 members allotted to all 50 states and the District of Columbia in proportion to their representation in Congress.
Each state, except Maine and Nebraska, awards its votes to the candidate who gets the most votes in the state. Maine and Nebraska split them by congressional district.
Here are some battleground states with their electoral vote totals, 2004 results and recent details about the contests in each state.
Colorado:Nine electoral votes. George W. Bush beat John Kerry 52 per cent to 47 per cent in the state in 2004, but since then, Democrats have won the state Legislature and governor's office. The four latest polls put Mr Obama up by between 4 and 7 points.
Florida: 27 electoral votes. Mr Bush beat Mr Kerry 52 per cent to 47 per cent in a state known for the disputed result that decided the 2000 election. Florida is a classic swing state with many older voters who could favour Mr McCain along with Jewish voters who are normally Democratic but have been wary of Mr Obama. Two new polls today had Mr Obama in the lead by 1 and 3 points respectively, while another recent poll gave a 1-point edge to Mr McCain.
Indiana:11 electoral votes. Mr Bush beat Mr Kerry by 20 points in 2004 in a state that last voted for a Democrat in 1964. But it borders Mr Obama's home state of Illinois and he has poured resources into his Indiana campaign after finishing a strong second to Senator Hillary Clinton in the May Democratic primary. The Reuters/Zogby poll today showed Mr McCain in the lead by 5 points, although earlier polls had showed the race as a dead heat.
Missouri: 11 electoral votes. Mr Bush beat Mr Kerry 53 per cent to 46 per cent in 2004 in a classic battleground with a mix of cities and conservative rural areas. The race looks to be among the tightest in the country, with two new polls today showing it a tie.
New Hampshire: Four electoral votes. Mr Kerry beat Mr Bush by 1 point in 2004. Mr McCain's history of big primary wins in New Hampshire in 2000 and this year gives him hope he can take the state in November. Democrats captured both the state's seats in Congress and gained control of the state Legislature in 2006 in an anti-Republican wave on which Obama hopes to capitalize. A poll on Sunday showed Mr Obama ahead by 11 points.
New Mexico:Five electoral votes. Mr Bush beat Mr Kerry by fewer than 6,000 votes in 2004. As the senator from neighboring Arizona, Mr McCain is familiar to many New Mexico voters, but he will have to battle Mr Obama for the growing bloc of Hispanics, who make up more than 40 per cent of the state's population. The most recent poll shows Mr Obama ahead by 10 points.
Nevada:Five electoral votes. Mr Bush beat Mr Kerry by 20,000 votes in 2004 in a state won by Republicans in eight of the past 10 presidential elections. As in New Mexico, the burgeoning Hispanic population will be crucial - it now makes up nearly a quarter of Nevada's residents. The Reuters/Zogby poll gave Mr Obama a lead of 11 points.
North Carolina:15 electoral votes. Mr Bush beat Mr Kerry by 12 points in 2004, even though the Democratic vice presidential nominee, John Edwards, was from the state. More than one-fifth of the population is black and an influx of transplants to high-tech urban areas have given Mr Obama a chance. The two most recent polls split, one showing Mr McCain up by 1 point and the other giving a similar lead to Mr Obama.
Ohio:20 electoral votes. Mr Bush beat Mr Kerry by about 120,000 votes in the state that ultimately decided the 2004 race. No Republican has won the White House without Ohio, and Mr McCain will have a hard time piecing together a win without the state. The Reuters/Zogby poll today gave Mr Obama a narrow 2-point lead in what appears to be a very competitive race.
Pennsylvania:21 electoral votes. Mr Kerry beat Mr Bush 51 per cent to 48 per cent in 2004, but Pennsylvania is one of a handful of states won by Mr Kerry where Mr McCain's camp had seen a chance to reverse the result. The two latest polls show Mr Obama up by 9 and 10 points respectively.
Virginia:13 electoral votes. Mr Bush won fairly easily by 9 points in 2004 in a state that has not gone Democratic in a presidential election since 1964. But Virginia has trended toward Democrats in recent state elections amid dramatic growth in the Democratic-leaning northern suburbs of Washington, DC. The Reuters/Zogby poll today had Mr Obama ahead by 7 points, while two other recent polls gave him a 4-point lead.