Ever since sophistication of technology and human desire for a better, more comfortable and luxurious life have started to converge, it has had a direct impact on the way engineering projects are approached and handled. This is especially true since the second half of the previous century. A natural consequence of this is that conventional project management approaches are increasingly coming under stress. One thing that can be generally assumed to have happened is the increase in project complexity. However, the understanding of complexity by professional bodies and academia still seems to be at an early stage. This affects all industries and sectors, be they civil, electrical, manufacturing, IT or any other. As an example, we can look at the process and energy industry, with the oil sector being a case in point. Easily accessible oil fields have long since been discovered forcing new reservoirs and discoveries to be made in remote areas, deep seas or in complex forms like tar-sands. This research was undertaken to increase understanding of the role of project complexity in project management and its influence on the chances of achieving a successful project. This study focused on application of the new TOE framework on identifying and understanding the different elements (fifty in our case) of complexity, how they can be potentially grouped together into clusters of influence (fourteen in our case), contributing towards the three dimensions of complexity (Technical, Organizational and Environmental). The separate effect of these three dimensions on five common success criteria of cost, schedule, quality, safety and future business prospects was investigated. Also, the computed complexity dimensions were compared with a general perception of these three dimensions in the experience of the respondents to see the extent of the fit. To do this a survey was distributed to project managers in the member companies of the NAP network, a competence network of the Dutch process industry. The online survey contained questions on the interviewees’ most recent finished project. Through the survey, data was acquired on 67 projects performed in the NAP network. This data was analyzed using descriptive statistics and multivariate statistical techniques. Owing to the characteristics of the data, non-parametric analysis technique was used. The results of the study show the potential usefulness of application of TOE framework in project management research. The relationships found also have practical implications for project management in the NAP network and the process industry. It was shown that project complexity negatively influences project success, with technical and organizational complexity playing the most significant part. It was shown that cost and schedule were two categories of success showing the most susceptibility to complexity, whereas quality, safety and future business prospects showed resiliency towards any kind of complexity to a large extent. From the literature review, several observations were compared with the results of the thesis, showing interesting moot points. Confirming (Kloppenborg & Opfer, 2002), all types of risk have been shown to be of influence on the project result. It has been shown that the opinion of (Thomas & Mengel, 2008) that expert project management has not been paid too much attention is also confirmed by our results. Lack of planning is also shown as potential cause of project failure as indicated by (Dvir, Shenhar, et al., 2003). The biggest surprise was to find that project size has no correlation with project result, thus disproving (Collyer & Warren, 2009).