What kind of oligarchy? As Gawker’s Hamilton Nolan explains, Gilens and Page’s findings provide support for two theories of governance: economic elite domination and biased pluralism. The first is pretty straightforward and states that the ultra-wealthy wield all the power in a given system, though some argue that this system still allows elites in corporations and the government to become powerful as well. Here, power does not necessarily derive from wealth, but those in power almost invariably come from the upper class. Biased pluralism on the other hand argues that the entire system is a mess and interest groups ruled by elites are fighting for dominance of the political process. Also, because of their vast wealth of resources, interest groups of large business tend to dominate a lot of the discourse.
http://www.policymic.com/articles/87719/princeton-concludes-what-kind-of-government-america-really-has-and-it-s-not-a-democracy