Purpose: The purpose of this thesis is to identify factors that cause delivery delays in warehouse companies during peak season. To accomplish the goal of the thesis, the purpose was broken down into two research questions:  1. What factors can cause delivery delays in 3PL companies? 2. How does the peak season influence delivery delays in 3PL companies? Method: The research design of this thesis is a case study research conducted. The empirical findings have been gathered of two different techniques of interviews and secondary data documentation from the case company to gain a holistic view of the issue. The empirical results were later compared with the theoretical framework in order to answer the research questions. Finding: The research establishes different issues that can be identified concerning delivery delays such as lead time, bullwhip effect, and management information system. These factors assembled were not discovered during the literature study because they were hidden areas that appeared during the case study. Additionally, the elements that are gathered via the interviews with the case company management and the statistical data clarified the difference in the impact level on the delivery performance in the case company. The identified factors were divided following the tool or method that can be used to gain control over. The tools and the other theories identified as solutions to gain control over the delivery delays occur during the peak season in the case company. Implications: The identified factors in the literature study are considered as common factors that can be applied to other 3PL companies. If 3PL companies are facing problems regarding delivery delays, they can increase control by investigating the tools and methods presented in this thesis. Contributions: There is limited research investigated on this subject regarding 3PL companies. Therefore, the factors that were identified throughout the case study could participate in discoveries within this field of study.  Limitations: The research was limited to one case company and solely one supplier in the case company. The answers presented in this research could increase the reliability and credibility if the authors were able to include observations in the investigation. Furthermore, the date that has been this research performed is based on the time of COVID-19 that limited the authors to gather more data about the subject.