In a year where overall upstream oil-and-gas transactions were down significantly from the previous year, the Eagle Ford shale formation in South Texas proved to be an active region for companies looking to make a deal. 2013's $137.7 billion in total upstream merger activity represented a 49 percent decline from 2012's total of $270.8 billion.

The Eagle Ford, however, was the hottest region in the country for upstream deals with at least $8.8 billion in transactions, including Devon Energy's $6 billion purchase of GeoSouthern's assets in the shale play, according to PLS Inc., a Houston-based oil-and-gas research firm. "2013 actually is a year in which upstream oil and gas M&A activity by and large reverted back to the mean of the last several years of activity, after adjusting for the megadeals," PLS Managing Director Brian Lidsky said in a written statement. "Overall, the market remains healthy with ample deal flow and a host of motivated buyers."

The Permian Basin in West Texas and the Rocky Mountains region were the second and third most active regions for oil-and-gas transactions in 2013, with $7.5 billion and $5.5 in deals respectively.

Media Coverage Resources:

"Eagle Ford led energy deals in 2013, despite national decline":

"Oil-and-gas deals increased in the Eagle Ford last year but declined overall":

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