| 基金项目： | The author is indebted to Eduardo Pontual Ribeiro （UFRJ/CADE） paper, as well as to Maria da Graqa Fonseca （IE-UFRJ）, Getulio da whose suggestions helped to improve an early version of this Silveira （IE-UFRJ） and the seminar participants at IPEA-Rio and IPEA-Brasilia. The thanks also go to Iraci Matos Vasconcellos （UERJ）, Heloisa Borges and Bruno Caselli （ANP） for their help with the data. A non revised version of this paper was presented at 8th International Industrial Organization Conference （British Columbia Univ., Vancouver, May 2010） and at 44th Canadian Economic Association Meeting （Laval Univ., Quebec City, May 2010）. |
