hi Venezuela, a national hydrocarbon policy revitalized interest in increasing gas production. Activities included evaluating the recovery of gas from mature fields, especially those with a history of pressure maintenance by gas injection. In some cases, high uncertainties existed in the accuracy of the historical data (e.g., fluid production and injection, initial fluid properties, and fluid composition), which led to difficulties in estimating remaining gas reserves and the formulation of reliable field-redevelopment plans. The problem of historical-data uncertainties in the rejuvenation of mature fields was studied, and a volumetric-balance analytical method was developed to estimate remaining fieldwide gas reserves in the face of data uncertainties.