Scaling is one of the most frequently stated problems in the oil industry, and scale inhibitors (SIs) are applied to prevent its formation. Organophosphonates are well-known types of SIs, particularly useful for squeeze treatments, which can be found as both non-polymeric and polymeric molecules. However, the performance of phosphonate-based SIs is often limited by poor compatibility with calcium ions. In addition, many phosphonated SIs exhibit poor seawater biodegradation. Therefore, there is still a need to develop effective SIs with reliable calcium compatibility, thermal stability, and environmental acceptability. A series of linear and branched phosphonated polyetheramines were synthesized. The final products were evaluated for their calcium carbonate (calcite) and barium sulfate (barite) scale inhibition performance using a high-pressure dynamic tube blocking rig at 80 bar and 100 degrees C. This study showed that the best phosphonated polyetheramines had excellent performance on both barite and calcite scale formation compared to some common commercial phosphonated SIs. In addition, all of the synthesized SIs showed superior compatibility with calcium ions and good thermal stability at 130 degrees C. The linear phosphonated polyetheramines gave the best seawater biodegradability, with BOD28 up to 47% by the OECD 306 procedure.