As we approached the middle of 2011, I noted in an article for my Foolish friends that, in my humble opinion, Austin, Texas-based Brigham Exploration was the optimum way to play the hot Bakken and Three Forks reservoirs of the prolific Williston Basin.

In part because they produce both natural gas and more lucrative oil, those reservoirs -- which are spread among North Dakota and Montana, along with portions of Canada's Manitoba and Saskatchewan provinces -- are still among the most enticing plays on the enlivened North American energy scene. But as Brigham was gobbled up for $4.4 billion by the end of 2011 to become part of Norway's Statoil (NYSE: STO), the question moves to today's best approach for investors to benefit from the prolific Williston Basin plays.

The answer doesn't come easily. You could start at the top with ExxonMobil (NYSE: XOM), which became active in the Bakken in 2010 when it acquired Fort Worth's XTO Energy. Or there's obviously Statoil, with which you could continue to benefit from the solid assets that Bud Brigham and his team acquired prior to ringing the cash register with the Scandinavian company. But there are many other operators hard at work in the play, and I'd like to tell you about three that I consider attractive.

Start with the little one
Perhaps because, as an erstwhile "Austinite," I watched Brigham Exploration figuratively take off once it moved its emphasis to the Williston as recently as 2007, I'll begin with the smallest member of the trio, Houston-based GeoResources (Nasdaq: GEOI). The company -- whose market capitalization comes to just more than $750 million -- operates through both exploration and acquisitions, primarily in the Bakken, the active Eagle Ford play in South Texas, and the nearby Austin chalk.

As I've noted with the Bakken, both the Eagle Ford and the chalk provide opportunities for liquids production, along with natural gas. Indeed, at the close of 2010, about 60% of the company's reserves were in oil, and 74% were proved developed. And since we're concentrating on opportunities in the Williston Basin, I'll simply note that GeoResources operates projects in both Williams County, N.D., and in eastern Montana.

The Bakken's biggest leaseholder
The next largest of my Bakken threesome is Continental Resources (NYSE: CLR). However, as it relates to our interest in the Bakken, the company -- whose market capitalization totals about $13.5 billion -- holds the industry's largest acreage position there, with more than 900,000 net acres. About 72% of that position is in the North Dakota portion of the Bakken.

Beyond that, Enid, Okla.-based Continental can lay claim to a number of operating firsts in the Williston: In 2010, it became the first operator to complete a paired Middle Bakken and Three Forks well. That feat followed by two years its drilling of the first horizontal well in Three Forks. In 2004, it had completed the first North Dakota well to be both horizontally drilled and stimulated by hydraulic fracturing.

Along with its Bakken and Three Forks program, Continental also operates in the Red River units -- which are also in Montana and the Dakotas, and include the Cedar Hills field, the seventh-largest onshore field in the lower 48 states. It is also drilling in the Niobrara, a part of the Denver-Julesburg basin -- another liquids-producing unconventional U.S. play that covers parts of Wyoming, Nebraska, Colorado, and Kansas. In addition, it is conducting successful operations in Oklahoma's Woodford plays.

From the Eagle to China
The overall largest of my Bakken trio, EOG Resources (NYSE: EOG), is also by far the most wide-ranging. With a market capitalization in excess of $28 billion, the company operates a Bakken program that includes both North Dakota and Manitoba, Canada. In addition, it is one of the more dominant participants (with well in excess of 500,000 net acres) in the Eagle Ford, and it is involved in the North Texas Barnett and Haynesville shales, the Niobrara, and the Texas portion of the Permian Basin. This array of activities allowed the company to achieve a whopping year-over-year hike of 64% in U.S. crude and condensate production during the third quarter of 2011.

Beyond its Manitoba portion of the Williston Basin, Houston-headquartered EOG's international activities include exploration, production, and marketing activities in other locations like the Republic of Trinidad and Tobago, the United Kingdom, and China. From my perspective, its operations in China present it with an intriguing leg up in that energy-thirsty developing country.

Don't neglect your own research
There are numerous other attractive companies operating in the Bakken and Three Forks reservoirs of the Williston Basin. My suggestion is that you perform careful analysis on the three companies described above, along with other Williston Basin operators that may tickle your fancy.

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