Stone Ridge Technology has introduced ECHELON, an ultrafast extended black-oil reservoir simulator supporting major engineering features. ECHELON runs on graphics processing units (GPUs), the current generation of which provides 5X or more memory bandwidth than central processing units and a similar advantage in computing throughput, both critical to a simulator’s performance. By combining the extreme computational power and bandwidth of GPUs with recent advances in solver algorithms and modern software design, ECHELON is able to achieve unprecedented run times with only a modest hardware footprint. With ECHELON, models up to 35 million active cells can now be run on a single desktop with turnaround 10 to 50 times faster than that of existing solutions that require big clusters. The ability to simulate very large models allows the use of highly detailed geologic descriptions without the need for upscaling. The fast run times and capability to handle very large models provide a powerful and cost-effective tool for engineers to handle multiple realizations for uncertainty quantifications.