In environmental impact assessment, qualitative methods are used because they are versatile and easy to apply. This methodology is based on the evaluation of the strength of the impact by grading a series of qualitative attributes that can be manipulated by the evaluator. The results thus obtained are not objective, and all too often impacts are eliminated that should be mitigated with corrective measures. However, qualitative methodology can be improved if the calculation of Impact Importance is based on the characteristics of environmental factors and project activities instead on indicators assessed by evaluators. In this sense, this paper proposes the inclusion of the vulnerability of environmental factors and the potential environmental impact of project activities. For this purpose, the study described in this paper defined Total Impact Importance and specified a quantification procedure. The results obtained in the case study of oil drilling in Colombia reflect greater objectivity in the evaluation of impacts as well as a positive correlation between impact values, the environmental characteristics at and near the project location, and the technical characteristics of project activities. •Concept of vulnerability has been used to calculate the importance impact assessment.•This paper defined Total Impact Importance and specified a quantification procedure.•The method includes the characteristics of environmental and project activities.•The application has shown greater objectivity in the evaluation of impacts.•Better correlation between impact values, environment and the project has been shown.