This study sought to propose a definition that gives a threshold for what should be termed a marginal field in Nigeria, as is obtainable internationally. The profitability of marginal field operators under the prevailing fiscal regime was examined. The impact of unexpected increase and drastic oil price drops on the performance of these fields was also investigated. An economic model was developed and stochastic simulation applied to account for risk and uncertainties. The findings of this study provided a working definition for marginal fields in Nigeria, as fields with reserve sizes of up to 30 MM bbls.