U.S. stocks declined on Friday, with benchmark indexes posting sizable weekly losses, as crude's ongoing slide rattled investors.
"This started a week or so ago, we'd recovered from the October low to a level that is arguably overvalued, and when we're overvalued everything has to go right, and what's not going right is what's happening to the price of oil, and what that means for Russia, Europe and the U.S.," said Hugh Johnson, chairman of Hugh Johnson Advisors.
"Everybody likes to say the price decline in oil is good news for the U.S. economy, but the real issue is this is really bad news for Russia, and by implication, bad news for Europe, which does a lot of business with Russia. The problems in Russia are getting transmitted to Europe, and Europe is an important trading partner for the U.S.," said Johnson.
"Whether it's by design or not, this is clearly putting pressure on Russia. This, plus the well-known sanctions have caused a recession in Russia, which is very dependent on oil" income," he said.
The Chicago Board Options Exchange Volatility Index, one measure of investor uncertainty, rose 5 percent to 21.08, up 78 percent this week.
Oil prices fell further after the International Energy Agency reduced its outlook for global demand.
"As prices have declined over the last month or two, we've also seen downward revisions that reinforce the price decline," said Kate Warne, investment strategist at Edward Jones.
Equities around the globe dropped on Friday after November Chinese factory production slowed more than forecast.
U.S. wholesale prices declined 0.2 percent drop in the producer price index in November after a 0.2 percent rise the previous month.
The drop in commodity prices could be seen in Friday's PPI, "it's showing up in lower inflation, and in the case of Europe, which is just a whisker away from deflation, that's not good news, because fiscal policy in Europe is leaning towards restraint. They believe in balanced budgets regardless. I don't, but they do. If they suffer deflation, that will disarm European central bank interest rate policy," said Johnson.
Adobe Systems gained after the software maker said it would acquire stock-photo company Fotalia for $800 million and posted quarterly results that beat expectations.
Stocks only briefly trimmed losses after a measure of in December exceeded expectations, rising to an eight-year high.
American consumers "are feeling better, and lower gasoline prices will continue to help sentiment, which should be good news for stocks overall, but today it's all about worries that lower demand for oil means slower growth in the rest of the world, and nobody is sure how big that slowdown will be," said Warne.
The Dow Jones Industrial Average declined 315.51 points, or 1.8 percent, to 17,280.83, down 3.8 percent from the week-ago close, its worst weekly loss since November 2011. International Business Machines led blue-chip losses that extended to all 30 components.
Recording its worst weekly hit since May 2012, the shed 32.99 points, or 1.6 percent, to 2,002.34, down 3.5 percent for the week, with materials falling the most among its 10 major industry groups, with all in negative terrain.
The Nasdaq declined 54.57 points, or 1.1 percent, to 4,653.60, off 2.7 percent from last Friday's close.
For every share rising, nearly four fell on the New York Stock Exchange, where 964 million shares traded. Composite volume neared 4.2 billion.
The U.S. dollar declined against the currencies of major U.S. trading partners and dollar-denominated commodities including gold and oil fell.
Crude futures for January delivery declined $2.14, or 3.6 percent, to $57.84 a barrel, settling below $58 a barrel for the first time since May 2009. The February gold contract fell $3.10, or 0.3 percent, to $1,222.50 an ounce on the New York Mercantile Exchange.
The yield on the 10-year Treasury note used to figure mortgage rates and other consumer loans dropped 8 basis points to 2.0810 percent.
On Thursday, U.S. stocks advanced, cutting weekly losses, but euphoria over increased retail sales in November faded as oil fell to another five-year low and renewed worries of a government shutdown.
"Stocks tend to move higher towards the end of the year, but we need oil to stop falling for the typically end-of-year feelings to take over," Warne said.