This paper presents the geothermal validation testing performed with the ECLIPSE™ industry-reference reservoir simulator using the Stanford geothermal test cases used to validate both TETRAD and TOUGH2 during early development. The ECLIPSE simulator software was able to match each of the test problems as accurate as the TETRAD or TOUGH2 simulators achieved. The evaluation of the results confirmed the modeling accuracy of ECLIPSE and demonstrated that the parallel processing capabilities of the ECLIPSE simulator can provide a 40× computational speed increase when operating in parallel vs. operating with a single processor. The models created with the ECLIPSE simulator demonstrated the software has the capability to accurately model typical two-phase reservoir conditions with countercurrent steam-water flow, well drawdown, cold water injection, and aquifer intrusion. The initial validation steps have been completed for utilizing the ECLIPSE simulator for geothermal reservoir modeling.