Oil and gas exploration in the Tarim Basin and Sichuan Basin has been gradually expanding to deep–ultradeep carbonate strata (> 8000 m). Three types of large-scale high-quality carbonate reservoirs have been found, including fault-dissolution reservoirs associated with fault–fluid coupling alteration, Cambrian subsalt dolomite and microbialite reservoirs, which are the most important hydrocarbon reservoirs to be discovered after karst fracture–cave and reef–shoal facies reservoirs. The deep–ultradeep Ordovician carbonates in the Tarim Basin were first broken and fractured by strike–slip faults and then partly dissolved by diagenetic fluids, such as meteoric water, hydrothermal fluids, and fluids derived from thermochemical sulfate reduction (TSR), leading to the formation of fault-dissolution reservoirs with coupled fault and fluid alterations. The granular dolomites of the Cambrian subsalt shoal facies are prone to leaching by quasi contemporaneous meteoric water to form high-quality dolomite reservoirs, which are rich in intergranular, intragranular, and intercrystalline pores and dissolution vugs. Microbialite reservoirs occur widely in the Upper Ediacaran Dengying Formation in the Sichuan Basin and the Qigebulak Formation and Lower Cambrian Xiaoerbulak Formation in the Tarim Basin. The microbialite reservoirs are mainly microbial thrombolites, stromatolites, and microbial reef mounds, which generally contain abundant framework pores, with porosities as high as 11.29%. A series of geological factors, such as oil and gas charging, high concentrations of CO2 and H2S derived from TSR, and fluid overpressure in subsalt, ensure that the porosity in ultradeep carbonates can be well maintained. One or more of these types of ultradeep carbonate reservoirs are predicted to exist at depths > 10,000 m.