* Oil falls more than $2 on China data, margin call change
* Euro hits six-week low versus yen on Greek woes
* Asian stocks mixed despite firmer commodities
MELBOURNE, May 10 (Reuters) - Oil prices slid on Tuesday as a bigger-than-expected Chinese trade surplus and a hike in trading margins for U.S. crude spread caution among traders about volatile commodity prices, while Greek woes cut the euro to a six-week low against the yen.
China posted its largest trade surplus in four months in April, swinging from a trade deficit in the first quarter, as exports hit a record on stronger global demand.
Optimism over the robust result was set to give a lift to European stocks, although gains were likely to be limited by lingering fears of a debt restructuring in Greece after a credit rating downgrade.
"Exports are much stronger, that's the basic thing.... Global demand is still pretty strong, a bit stronger than many people feared," said Tao Wang, an economist with UBS in Beijing.
Speculation that China may extend efforts to slow down its economy helped depress oil prices, already hit by a 25 percent hike in trading margins by the CME Group.
Chinese and U.S. officials are meeting in Washington to thrash out issues including China's grip on the yuan, and the trade surplus number could ignite fresh criticism from U.S. lawmakers.
NYMEX crude for June CLc1 tumbled $2.21 to $100.32 a barrel by 0545 GMT, erasing nearly half of a 5 percent rebound on Monday, while Brent crude LCOc1 fell 1.9 percent to $113.79 a barrel before moving back above $114.
A sharp drop in silver prices last week triggered a broader pullback in raw materials that had a domino effect on other risky assets such as emerging market equities, as some investors slashed big positions and went to the sideline.
The CME's move to make it more expensive for speculators to trade oil futures on margin, while not completely unexpected, added to a sense that a year-long steep climb in commodity prices is on hold for now.
Equities were mixed with Japan's benchmark Nikkei 225 up 0.25 percent, aided by a 1.7 percent jump by carmaker Toyota on reports that its output will return to normal earlier than expected. Stocks ex-Japan were flat, while markets in Hong Kong and South Korea were shut for a holiday.
Jitters over a possible second bail-out package for Greece trimmed the euro 0.5 percent to $1.4284, nearing a seven-week low of $1.4254 hit the previous day. Against the yen, the euro was at 115.07, its lowest since late March.
The euro's recent fall was accelerated by last week's commodity sell-off and Monday's move by ratings agency Standard & Poor's to cut Greece's rating to B from BB-, dragging it further into junk territory.
"In the short-term, there could be more unwinding of euro/dollar long positions due to negative news on fringe euro zone countries' debt problems," said Junya Tanase, currency strategist at JPMorgan in Tokyo.
But some analysts said the euro was unlikely to fall as sharply as it did a year ago when the Greek debt crisis hit financial markets, because there was now a safety net for indebted countries.
"Last year there was an imminent threat that Greece could default. But now, even though people are talking about the possibility that some countries could default in the future, there are no worries about immediate defaults," said JPMorgan's Tanase.
The oil price fall followed a volatile week of trading that saw U.S. crude prices fall from over $114 a barrel -- the highest level since 2008 -- to $94 a barrel.
The impact of the margin hike on oil prices may be less severe than on silver, which fell more than 30 percent in late April due to a succession of margin hikes,sparking a sell-off in other commodities.
Spot silver slipped slightly to around $37.56, while gold edged down to $1,507 an ounce.
China's main stock index was trading slightly higher, waiting on a slew of data on Wednesday, including inflation.
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blogs.reuters.com/hedgehub (Additional reporting by Ayai Tomisawa in TOKYO and Manolo Serapio Jr in SINGAPORE; Editing by Richard Borsuk)