The dollar hit late-March highs against a basket of currencies on speculation the Swiss National Bank would follow the European Central Bank in dropping deposit rates. A stronger greenback makes dollar-denominated commodities, including oil, less affordable for holders of currencies such as the euro. In China, stock prices slumped 5 percent, hit by regulatory worries and declining industrial sector profits.
"Low volume holiday trade, largely off on strong dollar and hard sell-off in Chinese equity markets," Jim Ritterbusch of Chicago-based oil consultancy Ritterbusch & Associates said in a commentary on oil.
WTI settled down $1.33 at $41.71 a barrel, trading just over 280,000 lots, Reuters data showed. Activity in WTI has dwindled since Monday's volume above 500,000 lots, which is typical of a busy day in oil. Benchmark Brent oil ended the session down 60 cents at $44.86.
For the week, WTI rose 4 percent and Brent less than half percent. But for the month, both were down about 10 percent. Analysts expect oil to enter more cautious trading next week ahead of an all-important policy setting meeting of the Organisation of the Petroleum Exporting Countries on December 4. While Opec is expected to stick to high output levels to defend market share, traders and investors are wary of recent comments by top crude exporter Saudi Arabia that it was open to working on price support measures with other oil producers. "The meeting promises to be very lively and acrimonious," David Hufton, analyst at London-based PVM, said. "There may even be walkouts ... and it could still spring a very unlikely surprise." Some Opec officials questioned an upbeat demand forecast from its researchers, expressing scepticism there will be a quick easing by 2016 of the global supply glut in oil.