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What: Eclipse Resources Corporation (NYSE:ECR), Baytex Energy Corp. (NYSE:BTE), Vanguard Natural Resources, LLC (NASDAQ:VNR), and Panhandle Oil and Gas (NYSE:PHX) all plunged more than 10% today. Fueling their free-fall was a 4% drop in the price of crude, which plunged after government data showed that oil inventories unexpectedly grew last week.

So what: According to the Energy Information Administration crude oil inventories grew by 2.6 million barrels this week. That shocked the market, which expected inventories to fall by 800,000 barrels. What this suggests is that there's still way too much oil in the market right now, which is signaling to the market that oil prices could really stay lower for longer.

The hardest hit by today's plunge is Eclipse Resources, which was down more than 20% on the day. It's a rather surprising plunge as nearly two-thirds of Eclipse Resources production is actually natural gas while only about 15% of its production is oil. Vanguard Natural Resources is also in the same boat as it's primarily a natural gas producer. Further, as an MLP most of Vanguard Natural Resources' oil production is hedged leaving it even less exposed to today's drop. Panhandle Oil and Gas, likewise, is a natural gas-focused company as 69% of its production is gas. Also worth noting is the fact that Panhandle Oil and Gas has a pretty solid balance sheet, so its built to weather the storm. Clearly, this is a case where investors are selling first and asking questions later.

Baytex Energy, on the other hand, is primarily an oil company with 82% of its total production is crude oil so its no surprise to see its stock down more than 14% today. Especially considering the fact that Baytex Energy is a Canadian oil producer, which hurts it even more as Canadian oil typically sells at a discount to U.S. oil because of pipeline constraints. As such, it is a bit more exposed to the oil downturn than the other three big movers today.  

Now what: When oil prices crash it typically takes the whole industry down with it, even those companies that are only loosely related to its production. It's a reminder of just how irrational the market can be when it's filled with uncertainty.

Matt DiLallo has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.