ResFrac optimizes operators' return on investment by providing the industry's only genuinely coupled hydraulic fracturing, wellbore, and reservoir simulator. The entire development life-cycle can be modeled in a single continuous simulation: from fracturing to production. Because ResFrac describes both multiphase flow and fracture reopening and propagation, complex sequences such as parent/child fracturing and production (with detailed description of frac hits), refracs, and huff and puff EOR can all be modeled. Users can quantitatively optimize landing zone, well spacing, parent-child relationships, cluster spacing, fluid volume, proppant volume, fluid and proppant type, refracturing, and/or EOR huff and puff schemes. ResFrac is used by small independents and supermajors alike, and has been applied across nearly every major American shale play: Permian, Eagle Ford, Bakken, SCOOP/STACK, Utica, Marcellus, Montney, Haynesville, and Vaca Muerte.