Many studies are dedicated to MOOCs, however there was no clear answer to what makes a particular MOOC popular. This study was an attempt to answer this question. Data about MOOC distribution was collected for this research, including category data, university types and MOOC platforms, data regarding MOOC popularity in different time periods, and regarding MOOC completion rates. It was determined that university type and MOOC category did not influence the number of enrolled students. However, Coursera and edX attracted many more students than the other MOOC platforms. Besides these facts, the number of students who really completed the course was much higher for the MOOCs created by top universities. Thus, courses by top universities did not have higher enrolment, however they became more well-known because of the number of students who really took them. The assessment format had a high influence on the completion rates as well. A traditional MOOC format and auto grading caused higher completion rates than other formats. Thus, popular MOOCs could be created in any category by each university, however Coursera and edX's courses attracted more students, and an auto grading course format involved them in studying the course.