The benefits of cementing systems containing high percentages of pozzolanic materials (abbr. “pozzolan” systems) were investigated and compared to conventional API cement systems at same densities. Besides the presentation of technical results based on laboratory tests, economical and ecological features were also considered. For the tested pozzolan systems up to 65% of the cement was substituted with sustainable minerals, resulting in a significantly reduced CO2 footprint and costs. Slurry performances (rheology, stability, and fluid loss control) as well as properties of the set systems (water permeability, compressive and tensile strength) were evaluated for various densities and temperatures. The results reveal that the pozzolan systems generally require lower additive dosages to adjust the desired slurry performances. Furthermore, strength and durability (towards retrogression and corrosion) are consistently more favorable for the pozzolan systems. Findings were related to the working mechanisms of the used pozzolans in cement systems. The study proves that improved technical performance, economics, and sustainability can be combined together in appropriately designed pozzolan systems.