U.S. stocks fell as tumbling oil prices sparked a broader selloff in equities, while Federal Reserve Chair Janet Yellen signaled increased confidence in the economy, laying the groundwork for a December interest-rate increase.

Equities continued a pattern of alternating between gains and losses that led the S&P 500 in November to its narrowest monthly move in six years. Energy producers today dropped the most in two months as crude fell below $40 a barrel for the first time since August, and raw-material shares had their biggest slide in three weeks. Technology companies erased early gains as Qualcomm Inc. and Yahoo! Inc. trimmed their rallies.

The Standard & Poor’s 500 Index declined 1.1 percent to 2,079.67 at 4 p.m. in New York, reversing yesterday’s 1.1 percent rally to open the month.

The S&P 500 extended losses in afternoon trading as crude’s decline accelerated before an OPEC meeting Friday. As three days of economic events likely to set the course for global markets into 2016 kicked off, traders’ focus on diverging monetary policies was diverted by a renewed rout in crude as OPEC has shown few signs it will vote to trim output.

Meanwhile, major central bank policies are set to diverge as European Central Bank President Mario Draghi has been priming markets for action since October. Economists surveyed by Bloomberg unanimously predict the ECB will boost stimulus again at its meeting tomorrow, while the bank is less than halfway through a 1.1 trillion-euro ($1.2 trillion) bond-buying program.

The S&P 500 has rebounded 11 percent from its low in August on growing confidence that the economy is sturdy enough to handle higher borrowing costs. The benchmark is up 0.9 percent for the year, and has alternated between gains and losses over the last 12 sessions, the longest such streak since 2013.

Source: Bloomberg