The shale oil and gas revolution originated in days of more encouraging hydrocarbon prices, but the ensuing technological advancements in horizontal drilling and hydraulic fracturing, as well as a better understand of the reservoirs themselves have acted to transform the Petroleum Industry over the course of the past decades, and will continue to do so for decades to come. The increased attention to unconventional shale oil & gas plays is a result of innovative engineering and increased knowledge driven by research and development, allowing for these resource rich systems to be unlocked. This thesis begins by introducing reservoir engineering concepts associated with shale oil and gas, including total organic content (TOC), gas desorption, non-Darcy flow, the Klinkenberg Effect (gas slippage), and the governing equations for naturally fractured systems. For evaluation purposes, reservoir simulation techniques continue to improve for unconventional applications, but shale plays have no oil-water contact and are found to be so vastly extensive, heterogeneous and naturally fractured that accurate reservoir models have not yet been developed and made available for shale reservoirs. In North America, the standard technique for oil and gas economic evaluation continues to be well decline curve analysis (DCA), utilizing type curves and economic considerations to calculate a set of static economic results. Further, a sensitivity analysis can be conducted for the base case to determine the impacts of each parameter on the economic results. This thesis builds on the concept by developing a model capable of calculating a new net present value (NPV) resulting from the simultaneous modification of any desired input parameter. This includes oil and gas prices, price differentials, gas shrinkage, capital expenditures (CAPEX), operational expenses (OPEX), water disposal costs, over ridding royalty, combined production and ad valorem tax rate, abandonment cost, and oil, gas, and water production rates. This evaluation method is referred to as the 'El-Aayi Technique' and is capable of promptly deriving possible economic outcomes for minor as well as major adjustments made to all desired input parameters, with results exhibiting a reasonable error. The El-Aayi Model is further developed to incorporate Monte Carlo simulation by assigning ranges, distributions, and correlations for all desired parameters. The results illustrate the P90, P50, and P10 net present value probabilistic results. Although this work demonstrates the El-Aayi Method applied for the determination of a new net present value from modifications made to any combination of economic and production parameters, the Technique can also be applied to compute alternative economic indicators including reserves, discounted net present value, and rate of return. For the purpose of this thesis, the El-Aayi Technique is demonstrated through a case study of the Delaware Basin's horizontal stacked shale play potential. The Method is performed on the Wolfcamp and a comparison is made with the overlying Bone Spring (and Avalon combined) formation. Data is limited by actively producing, horizontal wells with beginning production between January 2016 and June 2017. A comparative analysis of the plays is conducted demonstrating relative performance results associated with reserves, economic results, and key driver. The work conducted in this thesis has applications for oil and gas operators, consulting firms, and financial institutions involved in the economic evaluation of petroleum assets (i.e. acquisitions and divestitures). In particular, those charged with modeling cases with high uncertainty or sensitive economics may benefit most from utilizing the El-Aayi technique.