Using principles of fuzzy logic, some procedures are suggested to weight the maturity of geological environments of a hydrocarbon producing basin. The purpose is to generate an index of favorability for new investments in conventional exploration.The reasoning applied involves the following concepts:Consider the implicit subjectivity when assigning a certain degree of maturity to an entire basin or an environment of it.It uses more flexible linguistic variables than statistics to characterize ambiguous concepts of geology and other areas involved.Incorporates a wide number of variables. It allows grouping results of different valuations.