Voters have 10 candidates to choose from, making a runoff a near certainty because 50 percent of the vote is needed to become mayor. The top two vote-getters would face off June 7 if there's a runoff.

In the waning days before Tuesday's votes are counted, the candidates have forgone sleep to court voters at all-night restaurants and bars in a last attempt to persuade undecideds, and they've driven or walked through neighborhoods to offer to pick up and deliver ballots. It's too late for people to mail ballots and they must be dropped off at voter centers.

But Denver voters don't appear to be energized by the election, which has included a long cast of candidates, from councilmembers, a former state lawmakers and some long shots, such a resident who tried to get the city to form an extraterrestrial commission. The city's Elections Division said Monday that more than 298,200 ballots were sent out and so far about 67,400 voters have returned them. That's a turnout of about 22.6 percent.

"It's low. It's very low. There were so many candidates, you'd think it would be higher," said Tina Romero, of the Elections Division's communications department.

The polls close at 7 p.m.

Norman Provizer, a professor of political science at the Metropolitan State College of Denver, said all-mail elections usually help turnout. But this race been has been one "without a lot of buzz."

"None of (the candidates) has really ignited in the sense of capturing a lot of overt public attention," Provizer said.

All the top candidates are Democrats who don't differ much on major issues, Provizer said.

The candidates are vying to replace John Hickenlooper, who is now the governor.

The election has seen a wide divide among the candidates in terms of fundraising. That, in part, has led political observers to believe that the race hinges on three candidates: Former state Sen. Chris Romer, City Councilman Michael Hancock, and former Denver Public Schools Board member James Mejia, who also led the construction of the city's new justice center.

Romer has raised about $1.4 million, Hancock has raised $791,200, and Mejia has $571,300. By comparison, one of the closest competitors, Denver Councilman Doug Linkhart, has raised about $175,100.

The job the candidates are lobbying for is a tough one: The winner will have 60 days after the July 18 inauguration to close a $100 million budget deficit for 2012.