The influence that actors have in bargaining situations is an awful difficult issue to determine. A new method for measuring this type of influence, both on outcomes of decision making and on decision makers themselves, is presented. It involves a separate assessment of preference realization and the ascription of this realization to an actor. Both are assessed by means of qualitative data gathering, followed by paired comparisons of these data of the actors involved in order to find quantitative scores. This makes possible interval measurement, needed for the use of influence as one of the variables in sophisticated multi-variate data-analysis in quantitative research. The method is illustrated by a case regarding the influence of political actors involved in the Framework Convention on Climate Change.