The hydrogen index (HI) is a parameter obtained from Rock-Eval data which reflects general hydrocarbon generation and maturation trends in petroleum systems. In the Mississippian Barnett Shale, the hydrogen index was used to map general boundaries between regions of oil and gas generation within the extents of the formation. Hydrogen index values were obtained via Rock-Eval analyses of Barnett Shale core samples. In this system, HI values greater than 100 represent primarily oil generation and HI values less than 100 represent primarily gas generation. Secondary gas generation is indicated by HI values less than 50. In addition, the 100 HI line was utilized to establish part of the assessment unit (AU) boundaries for the 2015 assessment of shale gas and shale oil resources of the Barnett Shale in the Bend Arch-Fort Worth Basin Province. The AU represents the fundamental boundary used in the National and Global Assessment Project for the assessment of undiscovered oil and gas resources.