Numerous events cause delays to entire power projects’ completion timelines, leading to loss. This paper focuses on revealing the critical delay causes in Nigerian power projects and identifying the delay types such as excusable delay, compensable delay, critical delay, and concurrent delay from the different perspectives of owner and contractor. Based on the survey of the 84 industrial experts in power distribution and transmission projects in Nigeria, this study provides the mean score and rank of 39 delay causes. Among the causes, 14 are identified as critical in the Nigerian power project. The top three critical delay causes are corruption and bureaucracy in government, inadequate fund/budget allocation, and price fluctuation/inflation. Owner and contractor do not show the difference in classifying the 14 delay causes into excusable and compensable delays. However, there was a difference between owner and contractor in categorizing whether a cause is critical or not and concurrent or not. A different viewpoint of types of delay cause can lead to a dispute which may lead to other delays and losses, and thus it is meaningful to understand the types of delay perceived from owner and contractor. Even though the delay cause and types are different depending on an individual project, the results of this study serve as a reference and would be beneficial for the practitioners in the construction industry to help identify the delay causes to manage them effectively.