Obama and the indefatigable Romney have made separate calls to Americans to tip the vote in their favour.
Various US polls continued to show a neck-and-neck race on the eve of election day, and this created uncertainty among investors and US presidential election watchers over who will win the White House.
According to analysts, the most likely result on Tuesday night will be a close but clear victory for either Obama and vice-president Joe Biden, or Romney and his running mate, Paul Ryan.
Both candidates campaigned late into the night on Monday, acknowledging to their supporters during their separate election rallies that everything depended on getting their votes.
In short, whoever manages to get undecided electorates to vote for them on Tuesday will ultimately win the election.
"If we don't turn out the vote we could lose a lot of gains we've already made. Ultimately, it's up to you. You have the power," a hoarse Obama implored his supporters on Monday during an election rally in Cincinnati, Ohio, a key battleground state both candidates and campaigns made frequent stops at before election day.
Romney, on the other hand, also made mention there was a need for every eligible voter to cast their ballot on Tuesday.
"We have one job left and that's to make sure that on election day everybody who's qualified to vote gets out to vote. We need every single vote," said Romney, one of the richest Americans ever to be nominated for president.
In an interview with the Mail & Guardian on Monday night in Chicago, TJ Crawford, executive director and founding member of the Chicago Votes volunteer organisation, said voter turnout will play a huge role in deciding who gets elected.
"For instance, those who consider themselves independents and are not aligned to any of the candidates have the power to swing this election. We are not sure who they are going to vote for but they will be central in determining who goes to the White House. Our job as Chicago Votes is to get everybody who is a registered voter to go out and cast their ballot," said Crawford.
The presidential election will also be determined by the battleground states, with Ohio being perhaps the most important battleground state with 18 electoral votes.
Obama won Ohio in 2008, and for Romney the state of Ohio is very crucial as no Republican has ever won the White House without carrying the state.
His strategists said last night Romney would return to Ohio on Tuesday because without it, he would have to win every other battleground state to defeat Obama.
Both candidates were back in Ohio at the weekend in the final push to convince its mainly white working class electorate to go out and vote on election day.
US vice-president Joe Biden, former US president Bill Clinton and the US first lady Michelle Obama also made their stops in Ohio to campaign for the Democrats.
The Republicans also had their big guns out on the campaign trail – including former Republican presidential candidate and current US senator John McCain, the former US secretary of state Condoleezza Rice, and the controversial House of Representatives speaker John Boehner.
Obama's vote, according to analysts, is likely to come from African Americans, Latino immigrants, women's groups and minorities.
Obama is also likely to get the support of white working class groups in Ohio, especially those in the automobile industry who still laud his decision to bail out the car manufacturers Chrysler and General Motors, significant players in the US economy. He is also credited for using the levers of government to bolster the US economy, investing education and healthcare.
But supporters of Romney – the former executive at Bain Capital who has a net worth as high as $250-million – said the US needed a new direction after nearly four years of economic stagnation, massive unemployment, and record-setting debt coupled with government intrusion in the economy, which has paralysed the private sector.
His campaign strategists claimed Romney got things done and as a businessman created tens of thousands of jobs while at Bain Capital, the private equity firm he has since left but continues to receive large payments from.
But according to UK author and journalist Nicholas Shaxson, Romney's Bain Capital "bought companies, loaded them with debt and paid itself extravagant fees before bankrupting them and destroying tens of thousands of jobs".
Last night, there were fears the country might face the possibility of chaos if the presidential election remained too close.
Analysts said a tie might lead to the repeat of the disputed 2000 election.
Analysts said one candidate could win the popular vote but lose in the electoral college, as did Republican George W Bush 12 years ago, beating Democratic nominee Al Gore, causing a bitter legal fight that went to the US Supreme Court.
US presidential elections are decided not by a winner-takes-all national popular vote as is the norm in many democracies around the world. Instead, candidates compete in a state-by-state contest to win the 538 electoral college votes assigned to the 50 states and Washington, DC.
The Obama and Romney's campaign teams have already lined up legal teams in preparation for possible litigation after a close race.
Meanwhile, Obama is expected to attend the 2012 election night rally at the McCormick Place in Chicago, a massive convention centre not far from Grant Park where tens of thousands convened on the evening of the his election in 2008.
The first batch of election results will be released around 3am South African time on Wednesday morning.