NexGen Energy Ltd. announce that the largest drill program in the Company's history focused on optimizing mine development has begun at 100% owned, Rook I property, in the Athabasca Basin, Saskatchewan. The drill program results will be incorporated into a NI43-101 Bankable Feasibility Study, building on the successful outcomes highlighted in the Company's Pre-Feasibility Study ("PFS") which demonstrated the Arrow Project to be an exceptional development opportunity for NexGen, Saskatchewan and Canada. The development optimization program consists of a minimum 125,000 m using 10 diamond drill rigs focusing on three objectives: Convert High Grade Indicated Mineral Resources to Measured Mineral Resources: Approximately 71,000 m will be drilled at a spacing sufficient to support the conversion of the currently defined high-grade ("HG") Indicated Resource (currently 256.6 M lbs of U3O8 contained in 2.89 M tonnes grading 4.03% U3O8) to Measured Resource. Measured Mineral Resources represent the highest level of mineral resource estimate, providing a significant amount of technical detail on the FS mine plan, design and economics. Covert Inferred Mineral Resources to Indicated Mineral Resources: Approximately 54,000 m will be drilled to support the conversion of part of the currently defined Inferred Resource (currently 91.7 M lbs of U3O8 contained in 4.84 M tonnes grading 0.86% U3O8) to an Indicated Resource. Further conversion of Inferred to Indicated Mineral Resources will optimise the usable mineral inventory for the FS mine plan which can only incorporate Indicated or higher classification resources in compliance with the NI 43-101 guidelines. Given the strong continuity of mineralization seen at Arrow, the conversion of Inferred to Indicated resources since delineation drilling commenced has been very efficient and predictable. Geotechnical and Hydrogeological Characterization: Approximately 12,500 m of the 125,000 m will also incorporate the geotechnical and hydrogeological characterization of the rock mass in the areas of potential mine development and Underground Tailings Management Facility ("UGTMF"). This additional analysis will build upon the significant geotechnical, hydrogeological and metallurgical testing that has been incorporated into the PFS. The 125,000 m of drilling outlined above will be added to the existing 296,000 m of drill data collected to date by NexGen to form the basis of an FS which will incorporate an updated Mineral Resource Estimate and scheduled for release in H1/2020. The FS will increase design detail to a resolution necessary to support at a minimum a Class 3 cost estimate (AACE International standard). The objectives of the FS are as follows: Further optimization of the proposed development of the Arrow Deposit with respect to mine design (stope layouts, development, and production schedule) based on only Measured and Indicated mineral resources, Defining a level of design to support the comprehensive Environmental Assessment applications, Engaging with construction experts to optimize construction sequencing, utilization of pre-fabrication, offsite module assembly, and identify alternative opportunities to advance project development timelines, Continuing the advancement of the UGTMF design to optimize tailings density and further reduce tailings volumes enabling the opportunity to minimize the surface footprint of the mine, Leveraging opportunities for capital cost optimization while increasing confidence in the capital and operating cost estimates, Integrating innovative but proven mining, milling and environmental technologies and sustainable practices including the evaluation of alternative energy solutions to further increase NexGen's sustainability commitment.