The starting point of the thesis is that national CO2 policy options are complex. In other words, that there are non-economic factors that are play at the implementation of the CO2 options. Why do some CO2 options not materialize in the market, despite favorable economic conditions? Current methods for answering such questions are strongly embedded in financial assumptions and monetary units (e.g. the MACC). The statement is that complementary methods are needed that focuses on other factors. Experts are proposing the Y-factor (factors about 1. physical interdependencies, 2. multiple actors and 3. behavior), but the method lacks empirical evidence. The objective of the thesis is to gather empirical data to underpin the Y-factor. The chosen research perspective is a transition perspective and empirical data is collected through six case studies and in-depth interviews. Six policy options in six sectors are analyzed: 1. the heavy industry, 2. built environment, 3. energy production, 4. forestry, 5. agriculture and 6. waste. For each case study, 3 to 5 interviews are carried out, a total of 21 interviews are analyzed.