Internet surveys are becoming a major mode of data collection, but are not yet fully fit to replace more classical modes of data collection like telephone surveys. Mixed-mode surveys are offered as a promising solution. However, there is considerable evidence that when different modes are used different results are obtained. Data from different modes may be different because the modes themselves lead to different response processes, or because different questions are employed in different modes (either by tradition or due to mode specific optimization of the questionnaire). For instance, because of the memory problems associated with verbal communication, telephone designers often use unfolding, or polar (end) labeling of response categories. The goal of this research is to identify means to combine telephone and web survey results effectively, by choosing formats for asking questions that are less affected by mode, than are others. In a series of experiments we test multiple formats for asking questions (e.g. unfolding opinion questions in multiple steps vs. asking a complete question in one-step) within each of the two survey modes. These experiments compare the effects of different question formats across and within data collection modes. Data were collected using the respondents to the PPSM panel, who were randomly assigned to an Internet and a telephone panel. Within each panel the same series of split ballot experiments on question format were conducted. This design enables us to disentangle question format effects from ‘pure’ mode (web vs telephone) effects.