The impact of various anchor groups on adsorption behavior of AMPS (R) copolymers was studied. The anchor groups differ in anionic charge density. Copolymer adsorption and water retention of oil well cement slurries achieved from CaAMPS (R)-co-NNDMA in the presence of an acetone-formaldehyde-sulfite (AFS) dispersant were improved by incorporation of minor amounts (similar to 1% by weight of polymer) of acrylic acid (CaAMPS (R)-co-NNDMAco-AA),maleic acid anhydride (CaAMPS (R)-co-NNDMA-co-MAA), or vinyl phosphonic acid (CaAMPS (R)-co-NNDMA-co-VPA), respectively. Performance of these terpolymers was studied by measuring static filtration properties of oil well cement slurries at 27 degrees C and 70 bar pressure. All fluid loss additives possess comparable molar masses and show the same adsorption behavior and effectiveness when no other admixture is present. In the presence of AFS dispersant, however, adsorption of CaAMPS (R)'-co-NNDMA and hence fluid loss control is dramatically reduced, whereas effectiveness of CaAMPS (R)-co-NNDMA-co-AA is less influenced because of acrylic acid incorporated as additional anchor group. Even more, CaAMPS (R)-co-NNDMA-co-MAA combined with AFS allows simultaneous adsorption of both polymers and thus produces good fluid loss control. CaAMPSO"-co-NNDMA-co-VPA no longer allows adsorption of AFS dispersant. This was also confirmed by rheological measurements. The results show that, in a binary admixture system, adsorption of the anionic polymer with anchor groups possessing higher charge density is preferred. Surface affinity of the anchor groups studied increase in the order -SO3- -> -COO- -> vic-(-COO-)(2)-> -PO32-.