Throughout my career, I sought, through my research to understand how we can achieve a just political order. (Most of the research was pursued together with Norman Frohlich.) In doing this, our works pursued a number of narrow subquestions which we saw as requiring answer to understand the larger question. This led us to pursue both theoretical and experimental works to tackle these topics. It also led me to develop tools to design and run experiments on computers.
First, we pursued the issue of collective action. No understanding of how we can achieve a better society can avoid this question. Building on both Mancur Olson’s Logic of Collective Action, and Anthony Down’s An Economic Theory of Democracy, we challenged Olson's conclusions by showing the role of entrepreneurial political leadership.
We also concerned ourselves, from the beginning, with the limitations of self-interest as a basis for understanding choice. More positive research on the nature of fairness, justice and other values became the logical next target of our work. Much of my research is available in the manuscripts that are on my personal website: http://gvptsites.umd.edu/oppenheimer/
Along one path (pursued together with Norman Frohlich), my most general concern was understanding how to evaluate, measure, and explain differentials of governmental performance among the developed democracies.
This closely paralleled my interests in distributive justice.
Along the other path, my concern was more mainstream formal theory and experimental methods. Here I include my continued focus on questions of collective goods, N person Prisoner Dilemma games, experiments, and the empirical limitations of self interest. In applications I always had an eye to marrying normative, and game theoretic solutions.