Oilfield scale inhibitors have been used for many decades, mostly to fight carbonate and sulfate scaling. Many inhibitors are known, but only a few show good biodegradation to make them environmentally acceptable in areas with strict regulations, such as offshore Norway. Often high biodegradation is at the expense of other useful properties, such as thermal stability for high-temperature squeeze applications. We have now synthesized and investigated a new class of polycarbonate polymers with pendant anionic functional groups (carboxylate and phosphonate) as potential oilfield scale inhibitors. These polymers have a carbonate group in the backbone. Polymers with carboxylate and phosphonate side groups were prepared. We report here the scale inhibition performance of these polymers at 100 degrees C against both calcite and barite scaling at typical North Sea conditions in dynamic tube-blocking equipment, both before and after aging at 130 degrees C. The phosphonated copolymer gave very good performance against calcite scaling and showed good thermal stability. This polymer also gave a biodegradation of 36% in 28 days in seawater by the OECD 306 test.