The inequality of opportunities is a recurrent issue of brazilian higher education system, on account of the low rates of access to this level of education. This question becomes even more relevant in view of the recent expansion policies of the system, which in the 1990s and 2000 boosted the growth of vacancies, promoted its diversification and established educational inclusion strategies, with the goal of expanding the capacity of the system to include members of disadvantaged groups. This paper examines the hypothesis that the educational opportunities in higher education, in the context of the recent process of expansion, are associated with the selectivity of the institutions of education and the fields of study. We used the microdata of the ENADE (Exame Nacional de Desempenho dos Estudantes do Ensino Superior) 2005, which evaluated the performance of students in fields of education and technology. From these data we compared the socioeconomic, demographic and educational caracteristics for students from selective and not selective institutions in the different fields. The results indicate, in general, that both the access to the selective institutions and fields of study of greater prestige depends on the social origin and trajectory of the students, and that the selection effects are more relevant in relation to the fields of study than in the case of the selectivity of the institutions. More specifically, it was observed a trend of students of lower social strata occupy more often places in the fields of low prestige. There is also a tendency for lower income and parental education students preferentially occupy positions in areas of low prestige in selective institutions than in high-prestige fields in not selective institutions, i.e., the students of social profile and school trajectory more privileged resort to educational opportunities in areas of high prestige in non selective institutions. Finally, is recorded, in many cases, that students of strata with small representation in certain fields, such as the low-income students, browns and blacks in the technological field, women in areas typically male, such as engineering, and men in areas typically female, as pedagogy and languages, have higher chances of attending institutions selective, which suggests that effects of superselection in these areas.