The history of the Venezuelan oil industry has witnessed three significant periods of contract renegotiation. This paper argues that to a significant extent these renegotiations were the result of lack of progressivity in the tax structure, which made governments increase taxes in periods of increasing rents. However, the way the renegotiations were conducted during the 1960s and 1970s, as well as in 2004-2007 had a significant component of opportunistic expropriation, generating high uncertainty on property rights and investment decline, forcing nationalization. By Francisco Monaldi, nonresident fellow for the Latin America Initiative, and Osmel Manzano, principal economist, Inter-American Development Bank. Harvard Kennedy School of Government working paper, 2009.