Here's Why Falling Oil Prices Dropped These 3 Stocks as Much as 28.3% in December

Oil and gas producers aren't the only ones reeling from tumbling energy prices. Clean Energy Fuels, Green Plains, and U.S. Silica are struggling too

The sudden drop in crude oil prices, coupled with a volatile end of the year for the U.S. stock market, pushed shares of many energy companies lower last month. That included companies that don't sell a single drop of crude oil, gasoline, or diesel.

Shares of natural gas transportation:

Fuels pioneer Clean Energy Fuels fell 22.9% in December according to data provided by S&P Global Market Intelligence. The market data also shows shares of ethanol and protein producer Green Plains slid 19.3%, while shares of sand and specialty mineal supplier U.S. Silica tumbled 28.3%.

What specifically caused each company to take a tumble last month -- and can investors expect a rebound in 2019?

Clean Energy Fuels made a lot of progress in 2018. Past efforts to simplify the business began bearing fruit, allowing the company to deliver positive cash flow and earnings. It also paid off half of its debt, and launched a major program with backing from energy major Total to get more natural gas-fueled trucks on the road. That said, much of the company's rising prospects were being carried by rising energy prices for much of last year. Wall Street is worried that the sudden deterioration of crude oil prices in the fourth quarter may have derailed that momentum.

It makes sense on the surface. As diesel fuel becomes more expensive, natural gas as a transportation fuel alternative becomes more attractive. Similarly, cheaper diesel fuel may make the economic calculus a wash.

But while sliding energy prices could create a headwind for Clean Energy Fuels in 2019, it may not be enough to completely trash the company's growth plans. Many trucking fleets are considering switching to natural gas fuels because of clean fuel requirements looming over the horizon, notably in California, and diesel fuel may not be able to compete on carbon emission standards in some states within the next decade.

Similarly, there's a new global fuel standard for ocean-going vessels coming in 2020, which is expected to increase global demand for diesel fuel by at least 12 billion gallons per year. That could keep create a higher floor for diesel fuel than the market seems to be factoring in right now, and allow natural gas fuels to remain economically competitive.

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