* Flurry of factors combined to trigger big selloff
* Soros, Goldman sell call, rates, bin Laden death all cited
* Waves of computer-driven selling stunned traders
* No single factor sparked the price plunge
* Some funds lost 10-20 pct last week, fund managers say
May 9 (Reuters) - By Joshua Schneyer
NEW YORK, May 9 (Reuters) - When oil prices fell below $120 a barrel in early New York trade last Thursday, a few big companies that are major oil consumers started buying around $117.
It looked like a bargain. Brent crude had been trading above $120 for a month. But the buying proved ill-timed. Crude kept on falling.
"They were down millions by the end of the day, trying to catch a falling piano," an executive at a major New York investment bank said.
Never before had crude oil plummeted so deeply during the course of a day. At one point, prices were off by nearly $13 a barrel, dipping below $110 a barrel for the first time since March.
Oil's descent followed the biggest one-day price drop in silver since 1980 on Wednesday, after hedge fund titan George Soros was reported to be selling. Exchange operators raised silver's margin requirements, making it more costly to trade the metal and sending investors out of the market. Silver plunged by 20 percent, more by week's end. The rout unnerved some commodity investors.
Oil just doesn't fall by 10 percent in the course of a normal day, though. In commodities markets, oil is king, and its daily contract turnover, typically around $200 billion, is usually able to absorb even large inflows or outflows of investment.
The rare moves of $10 a barrel usually are set off by dramatic events -- the outbreak of the first Gulf War in 1991, or the collapse in 2008 of Lehman Bros bank, which both led to recessions.
Of course, there was major news last week. But the daring Pakistan raid that killed Osama Bin Laden had done little to shift the balance of oil markets on Monday.
In interviews with more than two dozen fund managers, bankers and traders, no clear cause emerged for the plunge in price. Market players were unable to identify any single bank or fund orchestrating a massive sale to liquidate positions, not even an errant trade that triggered panic selling, as seen in the equities flash crash last May.
Rather, the picture pieced together from interviews on Thursday and Friday is one of a richly priced commodities market -- raw goods have been on a five-month winning tear over all other major investment classes -- hit by a flurry of negative factors that individually could be absorbed but cumulatively triggered a maelstrom.
Computerized trading kicked in when key price levels were reached, accelerating the fall.
"It was a domino effect," said Dominic Cagliotti, a New York-based oil options broker.
The negative factors -- prominent cheerleaders turning bearish, some weak economic data, cheap money from the U.S. Federal Reserve ending by July, a lessening of political risk -- merely provide a backdrop for the waves of selling. What stands out is the way computers turned readjustment of positions in a huge and deep market into a rout.
THE COMPUTERS
Stunningly large jolts from so-called stop-loss trading amazed market traders. The automated sell orders were generated as oil crashed through price points that traders had programmed in advance into their supercomputers. In many cases, computer algorithms sold for technical reasons, as oil dropped through levels that, once breached, could trigger ever larger waves of selling yet to come.
The machine trading, based on subtly different but fundamentally similar, algorithmic models, eliminates the white-knuckles and potential human error involved in actively trading a volatile market, and increases anonymity. Instead of breeding hesitation, abrupt price drops can quickly prompt these machines to unload a bullish long position in oil, and build up a bearish short one instead.
Machine-led trading is one plausible thesis for another apparent market anomaly that occurred on Thursday. Exchange data shows that the total number of open positions in the oil market -- a number that would typically fall in a selloff -- instead rose. Normally, panicky funds selling oil en masse would cause total "open interest" numbers to shrink, as exiting investors closed out contracts. But some machines, following the market trend, may have gone further, by dumping long positions and quickly amassing sizable short positions instead.
"Computers don't care. Momentum just increases until nobody wants to stand in front of it," said Peter Donovan, a floor trader for Vantage on the New York Mercantile Exchange.
Some big Wall Street traders watched their own systems sell into the down trend but couldn't know for sure who had initiated the selling spree. They only knew that similar machines at other firms, from New York, to London, Geneva and Sao Paulo, would be automatically selling in much the same manner.
During Thursday's crash, such selling locked in profits that high-flying commodities traders have been accumulating for months. Some of Thursday's rout appears to have been more a product of the wisdom of crowd computing than of widespread human panic.
"We believe the magnitude of the correction appears in large part to have been exacerbated by algorithmic traders unwinding positions," Credit Suisse analysts wrote in a report.
High frequency trading and algorithmic trading accounts for about half of all the volume in oil markets.
BIG NAMES TURNED BEARISH
Some of the seeds for the rout were sown earlier. In April. Goldman Sachs' bullish team of commodities analysts, led by Jeff Currie in London, issued two notes to clients in rapid succession recommending they pare back positions. In one, the bank called for a nearly $20 dollar near-term correction in Brent oil, while maintaining a bullish longer-term outlook.
The closely watched money king, George Soros, who runs a macroeconomic hedge fund, had said for months that gold was pricey. Even online advisors to mom-and-pop investors such as The ETF Strategist had warned of a bubble in precious metals that could be ready to pop.
On Wednesday, the Wall Street Journal had reported the Soros Fund was selling commodities including silver, and four sources from other hedge funds told Reuters they believed Soros was busy selling commodities positions again on Thursday.
Silver markets already had suffered four days of carnage and ended the week down nearly 30 percent. But silver is a tiny market, much more susceptible to sharp price moves. Some traders suspect that big holders were cashing out of the least liquid commodity market first, before moving onto the big one - oil.
As crude crashed on Thursday, it dragged down every other major commodity. The Reuters Jefferies CRB index, which follows 19 major commodities, was on its way to a 9 percent weekly drop, the biggest since 2008.
Oil's selloff began in London, and accelerated as New York traders piled in.
A routine report on U.S. weekly claims for unemployment benefits spooked investors, showing the labor market in worse shape than expected. That fed a growing pessimism about the resilience of the global economy after industrial orders slumped in Germany and the massive U.S. and European service sectors slowed. Then the European Central Bank surprised with a more dovish statement on interest rates than expected, signaling its wariness about the euro zone outlook. The dollar rose sharply.
Before noon New York time, Brent crude oil prices were already trading down a jaw-dropping $8 a barrel.
Fourteen hundred miles southwest of New York's trading floors, on Texas refinery row, oil men were stunned by the drop, which played havoc with their pricing models.
"It was nuts. Our risk management guys were tearing up their spreadsheets," said a major U.S.