The majority of online research is now conducted via discontinuous online access panels, which promise high response rates, sampling control, access to populations that are hard to reach, and detailed information about respondents. To sustain a critical mass of respondents, overcome panel attrition and recruit new panel members, marketers must understand how they can predict and explain what motivates people to participate repeatedly in online surveys. Using the newly developed survey participation inventory (SPI) measure, we identify three clusters of participants, characterised as voicing assistants, reward seekers and intrinsics. Our results suggest that most online surveys are filled out by intrinsically motivated respondents that show higher participation rates, response effort and performance; incentives do not offer an important response motive.