Projects in the upstream, midstream, and mining (UMM) sectors present unique complexity. The Construction Industry Institute's (CII) Research Team 398 aimed at developing the criteria that define project complexity in the UMM sector, a matrix that describes the different levels of complexity and assign tools from the CII database that can be used to manage complexity. The eventual goal is to create a fit-for-purpose handbook for the UMM sector. This project is divided into phases; the first phase is to develop a complexity matrix for the UMM sector CII companies with more mature project management organizations. The team used convenience sampling and conducted interviews with owners and contractors for this purpose. The methodology also included reviewing literature from research into complexity, the characteristics of the UMM sector and incorporating the findings of other complexity models developed within and outside of CII. The result was a complexity matrix that includes factors relevant to all the three sectors. The vision for the next phase includes validating the current complexity matrix and identifying key information ("golden nuggets") for addressing complexity.