The biggest member of Big Oil, ExxonMobil (NYSE:XOM), has spent the past few months buying its way into increased representation in two of the world's major hydrocarbon plays: offshore Africa and natural gas produced from shale rock.

Its primary addition in the shale area has involved the pending acquisition of Fort Worth's XTO Energy (NYSE:XTO), a successful member of the independent producers contingent, which, along with the likes of Chesapeake Energy (NYSE:CHK), has been a leader among the companies involved in shale gas production. And while it's been a player in Nigeria, its latest salvo into Africa was to have involved a $4 billion expenditure for the properties of Dallas-based Kosmos Energy, off shore of Ghana.

Kosmos is largely a creature of the financial world, with a slug of its funding coming from U.S. private equity firms, including The Blackstone Group (NYSE:BX). In October, the firm agreed to sell its stake in the so-called Jubilee field to ExxonMobil for about $4 billion.

The sale would have given Exxon a 23.5% interest in the field. Almost immediately, however, the deal ran into headwinds from the Ghana government, which trotted out a number of possible buyers, including China's largest offshore operator, CNOOC (NYSE:CEO).

Part of the attraction of Jubilee lies in its potential position at the east end of a structure that may extend as much as 700 miles to the west, where a group that included Anadarko Petroleum (NYSE:APC) and Spain's Repsol (NYSE:REP) off Sierra Leone made a major discovery last summer. Soon after the Exxon deal was announced, it became abundantly clear that it was not being met with enthusiasm in the country.

Last week, the powers that be in Ghana sent a letter to Exxon that, according to The Wall Street Journal, indicated that the government "is unable to support an ExxonMobil acquisition of Kosmos's Ghana Assets." The letter went on to state that it is the intent of the state oil company, Ghana National Petroleum, to acquire Kosmos's assets in Jubilee "at a fair market value."

So it appears that ExxonMobil is being blocked from a purchase it has sought earnestly. While I'd suggest that Fools continue to watch this unfolding saga, I'd also urge them to consider Exxon an awfully attractive addition to their investment future.

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Fool contributor David Lee Smith doesn't own shares in any of the companies mentioned above. He does welcome your questions or comments. CNOOC is a Motley Fool Global Gains pick. Chesapeake Energy is an Inside Value pick, and the Fool owns shares of both it and XTO. The Fool has a disclosure policy.