NEW YORK (CNN/Money) - As if rising oil prices, a sluggish job market and jitters about earnings weren't enough, investors have something else to worry about: another prolonged dispute over who's president after Nov. 2.

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If what happened in 2000 happens again, and no clear winner emerges for weeks after Election Day, that would probably be a drag on stocks. In fact, some market experts say, the prospect of such uncertainty is already weighing on the market.

"I'm up to a one-in-three chance that we will not know for days who won the election," said Greg Valliere, chief strategist at Schwab Washington Research Group. "And it could really drag on through December again. It's a cliche but it's a true cliche, that markets don't like uncertainty."

Valliere is not alone in seeing a strong chance of a challenged election. Both political parties are far more prepared for election challenges in court than they were going into the 2000 election.

And with polls showing a close race, one non-partisan election watchdog, Electionline.org, reported this week that there's a strong possibility that recounts, lawsuits and other disputes could delay a clear winner for weeks.

At least one political pundit, columnist George Will, suggested this week it could be May 2005 before a clear winner is known.

The markets were weak throughout the six-week dispute over who won the 2000 presidential election.

The Standard & Poor's 500 lost 1.6 percent on Nov. 8, the day after the election when the uncertainty was first apparent to investors, and tumbled another 2.7 percent between Nov. 8 and the close of trading on Dec. 12, the day the Supreme Court issued a late-night decision that settled the election.

But even when the outcome was settled that night, it wasn't enough to turn markets higher.

The S&P lost another 1.5 percent the day after the Supreme Court decision, and stayed relatively flat through the transition period that ended with Bush's Jan. 20 inauguration. And of course the bear market that began in 2000 continued throughout 2001.

Valliere and some other analysts say some of the recent weakness in the stock market is already due to a growing possibility of another prolonged period of post-Election Day uncertainty.

"That may be one of reason (the Dow is) 9,800 -- maybe the markets have already begun to worry about the outcome not being known," said Valliere.

Of course, there's also rising oil prices, which act like a tax on consumers and can slow economic -- and earnings -- growth.

Other analysts said it's tough to handicap how much of the market's weakness is about election uncertainty, and how much is other factors.

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"What you see lately is due to uncertainty about the election, about oil supplies, about the war on terrorism," said Drew Matus, senior economist at Lehman Bros. "The sooner one of those uncertainty factors can be removed would be good for the markets. I'm not sure if people are counting on someone winning Nov. 2. Deep down in people's mind, they realize there's a good chance it won't be decided then."

Even though prolonged post-election uncertainty won't catch investors by surprise the way it did last time, there's relatively little reason to think markets will be more willing to shrug off the election challenges this time around, said Richard Suttmeier, chief market strategist at brokerage Joseph Stevens.

"I don't know how likely it is that (an uncertain outcome) is going to happen again," he said. "But if it does, we'll do what we did in 2000, and that is have a decline in the stock market because everything will be on hold."