Chesapeake Energy (OTC:CHKA.Q) is probably the best example of a key transition taking place in the U.S. oil and natural gas market. The company bought lots of land, but is now selling it off to focus on its best properties. Devon Energy (NYSE:DVN) and Anadarko Petroleum (NYSE:APC) are doing the same thing.

Land grab
When the U.S. energy market was at the start of the shale drilling revolution, companies were buying with virtual abandon just to stake out a claim. For example, ExxonMobil (NYSE:XOM) spent over $30 billion to buy natural gas specialist XTO Energy. Not only did that transaction get Exxon instant scale in the natural gas space, but XTO also brought with it important expertise in horizontal drilling and hydraulic fracturing.

At the time, the purchase seemed like a real winner. However, as natural gas supplies swamped demand the commodity's price collapsed to all time lows. That turned the XTO buy into a drag and led Exxon CEO Rex Tillerson to note that the purchase timing was, "off a year or two."

Exxon, however, is a giant and can absorb some pretty big mistakes. Smaller players don't have that leeway. For example, Chesapeake Energy loaded up on debt in its land grab. If natural gas prices had remained high there wouldn't have been a problem, but as the fuel's price fell so did the value of Chesapeake's land.

In the fourth quarter of 2012, Chesapeake wrote down the value of its property by a whopping $2 billion. That was basically the same time it announced that Carl Icahn's efforts to replace the company's CEO had succeeded.

Getting back to business
In an effort to get Chesapeake back on track, the company has been selling assets. The purpose of the sales is two-fold: reduce debt and refocus around the assets with the best prospects. Although the company appears to be on the right track, some industry watchers have suggested Chesapeake sold too cheaply. That can happen when you're a motivated seller, and shows the inherent risk of the buying binge that happened throughout the oil and natural gas industry.

Anadarko Petroleum is another company refocusing around its best properties. It's most recent transaction was the $1.1 billion sale of Chinese assets. That comes on top of the mid 2013 sale of Mozambique assets for $2.6 billion. That sale was the capstone on Anadarko's $4.5 billion of divestitures in 2013.

During the company's fourth quarter conference call, CEO Al Walker described Anadarko as an active portfolio manager. The same thing is going on at Occidental Petroleum (NYSE:OXY) and Devon Energy.

Three of the four areas Occidental is focusing on are in the United States. The company is, "executing a focused drilling program in our core areas" to improve returns. Continuing to refocus on core assets, the company just announced the $1.4 billion sale of natural gas lands in Kansas, Oklahoma, and Colorado.

Devon Energy has gotten in on the act, too, just announcing the sale of Canadian assets for nearly $3 billion. CEO John Richels noted that the, "...agreement represents a significant step forward in the execution of our non-core divestiture process..." and that this sale, "...accelerates the refocus on core assets."

More than a fad
Clearly, there's more than an industry fad going on here. U.S. drillers are whittling their portfolios down to focus more on key properties. And while some of these players, including Anadarko, have notable foreign operations, all of them appear to like their U.S. assets enough to designate select domestic areas as core to their respective futures.

If you own oil and natural gas drillers watch the divestiture trends. Make sure the companies you own are keeping up with the Jones' on the profitability and efficiency fronts. Asset sales are an increasingly important part of that.

Here's a company helping drillers get even better...

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