* Markets go into "complete risk-off mode" as Trump leads polls
* Oil prices and dollar tumble, gold rallies as Trump goes ahead
* Analysts cite "Brexit deja vu" and "shock" as Trump leads
* Some benefit from crude rout: Fuel oil margins turn positive  

Oil prices tumbled on Wednesday as vote counting showed Donald Trump edging ahead in an unexpectedly tight US presidential election, throwing world markets into turmoil in a result reminiscent of June's Brexit vote.
Crude futures markets roared into action, with trading accelerating as Europe joined Asia from around 0500 GMT, as Trump surprised by defeating Democrat Hillary Clinton in a series of key contests and opening a path to the White House.
US West Texas Intermediate (WTI) crude futures fell to a session low of $43.07 per barrel, down more than 4 percent from their last close and their lowest since September, before edging back to $43.72 a barrel by 0601 GMT.
International Brent crude futures were down 2.43 percent at $44.92 a barrel.
"This is deja vu of the Brexit moment, very worrying," said Bob Takai, president at Sumitomo Corp Global Research in Tokyo, referring to Britain's surprise vote to leave the European Union in a referendum last June, which led to market turmoil.
The falls in oil came as prices for gold, a traditional safehaven for investors in times of high economic risk jumped, while the dollar fell sharply against a basket of other leading currencies.
"Investors moved into complete 'risk off' mode... Trump winning would have negative consequences on the price of oil," said Jameel Ahmad, vice president of market research at trading platform and research firm FXTM.
"The threat of growth forecasts being downgraded at least over the short-term due to investor uncertainty in theory weakens demand for commodities like oil."
Trump won the key battleground state of Ohio, Florida, North Carolina, and likely Georgia, and led Clinton in a series of other states that were too close to call.
"In financial markets, Trump's victory is seen as a 'shock', prompting to seek safe-haven assets and this has pushed oil prices down," said Son Jae-hyun, Seoul-based analyst at Mirae Asset Daewoo. In the longer-term Trump's pro oil sector policies and anti-Iran views could result in higher prices, he added.
Elsewhere, a report by the American Petroleum Institute (API) showed crude inventory figures rising by 4.4 million barrel was also weighing on markets.
There are also surprise beneficiaries from Wednesday's developments.
The tumble in crude oil prices pushed Singapore's fuel oil refinery margins, traditionally a loss-making business, into positive territory for the first time since 2012 as refiners benefit from cheaper feedstock prices.