Throughout 2010, Petrohawk Energy (NYSE: HK) has been selling off assets outside its two core areas of focus: the Haynesville shale and the Eagle Ford shale. The company also sold half of its Haynesville natural-gas gathering and treating business to Kinder Morgan Energy Partners (NYSE: KMP). All told, these sales brought in nearly $1.5 billion. Last week's disposition of all Fayetteville assets, including its gathering infrastructure, to ExxonMobil (NYSE: XOM) for $650 million takes the grand total to $2.1 billion.

One question you might ask is: Why the Fayetteville? Isn't that where Southwestern Energy (NYSE: SWN) has made a killing over the years?

Indeed it is. But the Fayetteville was never going to be a home run for Petrohawk, mainly because the company paid too much for entry. Between its two disclosed purchases in the late 2007-early 2008 time frame, including 24,000 net acres picked up from Contango Oil & Gas (AMEX: MCF) and its partners, Petrohawk shelled out $565.5 million for just 42,500 net acres, plus a pipeline gathering system. Petrohawk's Fayetteville acreage was last reported at 157,000 net acres, so it looks as if the company spent more -- and possibly quite a bit more -- in amassing its position than ExxonMobil is paying today.

Another even more fundamental question to ask is: Why is Petrohawk selling so much stuff? Part of the answer seems to be that it's focusing on its highest-rate-of-return opportunities to maximize value. I love to see management teams ditching non-core businesses to focus capital and attention on the best opportunities. But that's not the entire story here. Petrohawk also has a habit of spending way beyond its cash flow.

Through the first nine months of this year, Petrohawk's operating cash flow (i.e. before changes in working capital) was $535 million. Oil and natural-gas capital expenditures were $1.7 billion. Tack on other operating property and equipment capital expenditures, and you're over $1.9 billion. Petrohawk's revenue was only $1.2 billion.

Following last year's dramatic dilution at Petrohawk, I don't think investors would have been receptive to yet another equity offering -- especially at this year's depressed prices. That left asset sales as the go-to source of cash to cover the budget shortfall.

Now that the cupboard's become pretty bare, Petrohawk really needs its core assets to shine. If they don't, the company won't have much choice but to finally dial back on its multiyear spending spree.

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Fool contributor Toby Shute doesn't have a position in any company mentioned. Check out his CAPS profile or follow his articles using Twitter or RSS. The Fool has written puts on Contango Oil & Gas, and Motley Fool Alpha has written puts on Southwestern Energy. The Fool owns shares of Contango Oil & Gas and Exxon Mobil and has a disclosure policy.