Many business leaders agree that their performance depends on the quality of the service they provide and its impact on customer satisfaction. In order to survive in the market or to increase their market share, parcel service providers need to be aware of the key factors that affect customer satisfaction with parcel services. The aim of this article is to analyse customer satisfaction with parcel locker service theories, and create a theoretical model to identify the main reasons for customer satisfaction with parcel locker services. The research problem: What are the main reasons for customer satisfaction with parcel locker services? The research methods are based on scientific literature, and data was collected through the questionnaire survey method and analysed by AcaStat software. The theoretical analysis distinguishes the six main reasons for customer satisfaction as price and quality, location dimension, time suitability, technological friendliness, service reliability, and safety. The research data were collected from 438 parcel service delivery users in Lithuania. The results indicate that the main reasons for customer satisfaction are: no need to wait for delivery at home, easy-to-use parcel lockers, 24/7 service possibility, and location convenience. This research is limited, because it was carried out during the pandemic, and the results would need to be verified if the epidemiological situation changes.