By Ben Levisohn

A day that started off badly for stocks has gotten worse, as oils slide pulls down the shares of energy companies like Noble Energy (NBL ) and Anadarko Petroleum (APC ).

Getty Images

The S&P 500 has fallen 1.7% to 2,023.40, while the Dow Jones Industrial Average has dropped 303.95 points, or 1.7%, to 17,529.04. The Nasdaq Composite has declined 1.4% to 4,662.24, and the small-company Russell 2000 has dipped 0.9% to 1,187.59.

Looking for a reason? Start with oil prices, which briefly fell below $50 a share barrel today. causing oil stocks to plunge. Noble Energy (NBL ), for instance, has plummeted 9.2% to $42.56 at 12:52 p.m. making it the biggest loser in the S&P 500. Anadarko Petroleum (APC ) has tumbled 8.2% to $75.53. Throw in renewed fears that Greece could exit the European Union. and you have the recipe for a selloff.

Ned Davis Researchs John LaForge and Warren Pies think the pain in commodities will go on for a very, very long time:

Many more years of commodity deflation is likely. If history is any guide, another 16 years. The average bear market lasts 20 years. April 2011 was the likely peak this cycle, which puts us around year four of twenty

If oil prices stay low, within energy, we’d expect Refiners and Infrastructure MLPs to perform the best. Infrastructure MLPs because they are the least sensitive to oil swings. Refiners often benefit when crude oil prices decline, as oil is their main input costOn average, Refiners outperform the Energy Sector by almost 10% over the twelve months post the oil decline.

Why are small caps holding up better than the overall market? Evercore ISIs Dennis DeBusschere chalks it up to their lack of exposure to global turmoil:

Commodity prices remain under pressure this morning as global growth continues to moderate. As we enter 2015 U.S. growth remains strong relative to the rest of the world, leaving us in favor of non-commodity cyclicals and U.S. small caps. European risk is difficult to handicap ahead of the Greek election and the ECBs QE decision on January 22 nd. Unless it becomes clear Europe is headed for a credible open ended program we will continue to favor U.S. risk over Europe.

Wells Fargo: Time to Take a Breather Next

JPMorgan: Better in Bite Sized Bits?