The economic theory of the firm has met an exponential growth in the last decades different from the traditional neoclassical approach. In the first part of the paper we are skimming through the most spread approaches, namely the theory of incomplete contracts and evolutionary school. In the second part we apply the explications on integration provided by the economics of transaction costs with an example on the oil industry in Romania. A brief qualitative analysis reaches out the conclusion that cutting transaction and agency costs is one of the factors that leads to integration within the studied sector.

Transaction Cost, Agency Theory, Oil