* Market focuses on oil supplies, OPEC meeting on June 22
* U.S. weekly crude inventories seen lower - Reuters poll (Updates with comment, refreshes prices; changes dateline from SEOUL)
LONDON, June 5 (Reuters) - Brent crude futures eased on Tuesday, giving up early gains, as investors weighed the chances that global supply will increase substantially if OPEC decides this month to raise output, just as U.S. production grows at near-record rates.
Brent crude futures fell 11 cents to $75.18 a barrel by 0924 GMT, having lost 2 percent the previous day. U.S. West Texas Intermediate crude edged up 30 cents to $65.05.
"(The output decision) is going to be the main event of the month and the main input for the second half of the year, so any change in OPEC policy is a big event," Petromatrix strategist Olivier Jakob said.
Fund managers this year racked up a record bet on a continued rise in oil prices, but the sustained increase in U.S. shale production and now the prospect of higher OPEC supply have prompted many investors to pare those positions.
The premium of the Brent 2018 December futures contract over the December 2019 contract has shrunk by a third in a month to around $3.74 a barrel as investors became less bullish.
The Organization of the Petroleum Exporting Countries meets in Vienna on June 22 to decide whether the group and non-OPEC producers, including Russia, should raise output to make up for any supply shortfall from Iran and Venezuela.
"It's all about supply, whether it's OPEC raising output or the U.S. increasing production. All roads lead to higher global oil supplies, which is leaving oil traders shaking in their boots," said Stephen Innes, head of trading for Asia-Pacific at futures brokerage OANDA in Singapore.
Global oil supply has tightened with the OPEC-led production cuts that began in early 2017.
Crude stocks in the United States, the world's biggest oil consumer, were forecast to have fallen about 2.5 million barrels on average in the week ended June 1, according to five analysts polled before the release of weekly inventory reports.
But increasing U.S. production has put pressure on prices.
In March, U.S. crude output rose to 10.47 million barrels per day, the highest on record, according to the government's Energy Information Administration (EIA).
The American Petroleum Institute, an industry group, releases data on last week's U.S. oil inventories at 2030 GMT on Tuesday. The EIA report is due at 1430 GMT on Wednesday. (Additional reporting by Chung in SEOUL and Roslan Khasawneh in SINGAPORE; Editing by Dale Hudson)