Existing production in Fallon County is along the Cedar Creek Anticline. The anticline runs roughly from the NW to SE across the northern half of Fallon County. The Cedar Creek is an oil play. Prior to the recent Bakken play, the Cedar Creek was the largest oil producing area in Montana. Fallon County also has shallow natural gas production. Much of this is along the SW edge of the Anticline.
Denbury Resources (was Encore) is the primary producer in Fallon County. ConocoPhilips (was Burlington Resources) and Continental Resources are the other two larger players in oil production. Finally, Fidelity Exploration is the primary producer of the shallow natural gas fields in the county.
Looking ahead, Denbury Resources has plans to build a pipeline carrying CO2 from Wyoming into far SE Montana for enhanced recovery there (in Powder River Co). They've indicated after that is established they may extend the pipeline up to Fallon Co. for CO2 injection into the Cedar Creek formation as well. However if this is done, it would likely be four or five years from now before it could be completed. The first leg of the pipeline has not been built yet. Nor is it certain that Denbury has adequate CO2 supplies to provide for the project in both counties.
Recently there has also been some interest in exploring to the north and east of the anticline along the Fallon Co. & Wibaux County line. There has been some leasing on this play. However, I don't believe anyone has attempted to drill there yet (in recent years).