Peer-to-peer (P2P) carsharing services offer a promising strategy for sustainable mobility, yet their uptake in Sweden has been slower than anticipated, particularly among car owners functioning as service providers. This study seeks to address this gap in understanding by examining the factors influencing these car owners' decisions to participate in P2P carsharing services. Using the Fogg Behavior Model (FBM) as a theoretical framework, 13 semi-structured interviews were conducted with both active and inactive users. Findings reveal that financial incentives, trust, and the potential to contribute to environmental sustainability motivate participation, while concerns about vehicle damage, liability issues, and perceived low demand present barriers. These insights can guide the development of digital services to better address these factors, potentially stimulating broader participation. Future research, drawing on the FBM, could focus on designing effective triggers based on these identified motivators and barriers. Despite the potential limitation of the small sample size impacting generalizability, the study offers valuable implications for service designers  aiming to boost the adoption of P2P carsharing services in Sweden to achieve the country's emission reduction targets.