Due to the complex structure of the transportation systems, disruptions in transport operations may occur from time to time. In liner shipping, it is seen that shipping lines frequently deviate from the transit times announced in their vessel schedules, and this leads to schedule unreliability. This leads to schedule unreliability and affects all stakeholders. Based on actual transportation data, this study aims to evaluate the transit time reliability performance of shipping lines and the factors that may affect transit time reliability to investigate schedule reliability in liner shipping. To evaluate the transit time reliability of shipping lines’, transit time deviations were calculated based on observations containing 5080 transport data of shipping lines and current performances are discussed. Hypotheses were tested with independent sample t-test and Welch’s ANOVA to examine the factors affecting transit time reliability. Tamhane’s T2 post-hoc test was used to determine the difference between groups. Results show that transit time reliability of shipping lines is low. It has been observed that the type of service, season, vessel age, and TEU capacity of the vessel factors affect the transit time reliabillity. With this study, shipping lines can evaluate their reliability performances according to the competition. At the same time, lines can use these results to understand, evaluate and manage factors that affect their transit time reliability. In this direction, suggestions have been made to the shipping lines to contribute to improving transit time reliability and service quality. This article is regarded to close the gap in evaluating transit time reliability in liner transportation because it relies on actual transportation data.