Samples of gas, oil, and water were collected from shallow (<1,051 m) Wilcox Group (Paleocene-Eocene) coal and sandstone reservoirs and from under- and overlying Late Cretaceous and Eocene carbonate and sandstone reservoirs in northern Louisiana.  Isotopic data from seven Wilcox coal-gas samples indicate that the coal gases are primarily generated by bacterial reduction of CO₂.  The gas samples have average d¹³C_CH4 values of -62.05‰ PDB, and average dD_CH4 values of -187.9‰ SMOW.  Eight gas samples collected from conventional gas and oil wells suggest that both biogenic and thermogenic gases are present in and adjacent to the stratigraphic intervals that contain biogenic coal gases.  The mixed gases have d¹³C_CH4 values that range from -59.4 to -32.72‰ PDB, and dD_CH4 values that range from -180.8 to -131.9‰ SMOW. 

Two Wilcox oil samples produced from sandstones within the coal-bearing interval have geochemical characteristics comparable to published Wilcox oil data of the region including a pristane/phytane ratio of about 2, and similar d¹³C values for the saturate and aromatic fractions.  The oils are probably sourced from thermally mature, down-structural-dip parts of the Wilcox Group.  Gas chromatograms of the C₁₀₊ saturated hydrocarbons show a depletion of n-alkanes that probably indicate groundwater washing of the oil in these shallow reservoirs.

Isotopic data from four samples of produced saline water collected from oil, conventional gas, and coal-bed gas wells have dD_H2O values that range from -27.3 to -15.9‰ SMOW, and when compared to dD_CH4 values from the same wells, suggest that CO₂ reduction may be an important gas generation process in this system.