Social impact assessment (SIA) has become an important factor for social conflicts prevention. In this study, we conducted SIA using the center-point triangular whitenization weight functions (CTWF) method, which is based on grey systems theory. A case study was conducted on a hydrocarbon exploration project located in the Gulf of Valencia, Spain. Two stakeholder groups and four evaluation criteria were identified. The results revealed that for the group of the directly linked population, the project would have very negative social impact; and for the group of indirectly linked citizens, the project would have negative social impact. The results could help central and community governments to make the best decision on the project. The method showed interesting results and could be apply to SIA of other projects or programs.