New coal-gas exploration and production in northern Louisiana and south-central Mississippi, Gulf of Mexico Basin, is focused on the Wilcox Group (Paleocene–Eocene), where the depth to targeted subbituminous C to high volatile C bituminous coal beds ranges from 300 to 1680 m, and individual coal beds have a maximum thickness of about 6 m. Total gas content (generally excluding residual gas) of the coal beds ranges from less than 0.37 cm³/g (as-analyzed or raw basis; 1.2 cm³/g, dry, ash free basis, daf) at depths less than 400 m, to greater than 7.3 cm³/g (as-analyzed basis; 8.76 cm³/g, daf) in deeper (> 1,500 m) parts of the basin. About 20 Wilcox coal-gas wells in northern Louisiana produce from 200 to 6485 m³ of gas/day and cumulative gas production from these wells is approximately 25 million m³ (as of December, 2006). U.S. Geological Survey assessment of undiscovered, technically recoverable gas resources in the Gulf of Mexico Coastal Plain, including northern and south-central Mississippi, indicates that coal beds of the Wilcox Group contain an estimated mean total 109.3 million m³ (3.86 trillion ft³) of producible natural gas.

To determine the origin of the Wilcox Group coal gases in northern Louisiana, samples of gas, water, and oil were collected from Wilcox coal and sandstone reservoirs and from under- and overlying Late Cretaceous and Eocene carbonate and sandstone reservoirs. Isotopic data from Wilcox coal-gas samples have an average δ¹³C_CH4 value of − 62.6‰ VPDB (relative to Vienna Peedee Belemnite) and an average δD_CH4 value of − 199.9‰ VSMOW (relative to Vienna Standard Mean Ocean Water). Values of δ¹³C_CO2 range from − 25.4 to 3.42‰ VPDB. Produced Wilcox saline water collected from oil, conventional gas, and coalbed gas wells have δD_H2O values that range from − 27.3 to − 18.0‰ VSMOW. These data suggest that the coal gases primarily are generated in saline formation water by bacterial reduction of CO₂. Shallow (< 150 m) Wilcox coal beds containing freshwater have little or no biogenic gas.

Molecular and isotopic analyses of gas samples collected from conventional gas and oil wells suggests that both biogenic and thermogenic gases are present in and adjacent to the Wilcox intervals that contain biogenic coal gases. Oil, probably sourced from thermally mature, down-structural-dip parts of the Wilcox Group, is produced from sandstones within the coal-bearing interval. Gas chromatograms of C₁₀₊ saturated hydrocarbons from Wilcox oils show a depletion of n-alkanes probably resulting from biodegradation of the oil. Isotopic composition of the gases associated with the oils is of mixed themogenic and biogenic origin (average δ¹³C_CH4 = − 44.4‰ VPDB, and average δD_CH4 = − 182.4‰ VSMOW).