The synthesis of two carbamoylmethylphosphate (CMP)- and -phosphine oxide (CMPO)-tetrafunctionalized cavitands with a propyl spacer between the cavitand platform and the chelating sites is described. Liquid-liquid extractions with CMP(O)-and N-acyl(thio)urea-tetrafunctionalized cavitands were performed from aqueous nitric acid into dichloromethane or o-nitrophenyl hexyl ether (NPHE). The extraction of americium (III) and europium (III) from aqueous nitric acid into NPHE was studied in both the absence and presence of Br6-COSAN as a synergist. CMP(O) cavitands are more efficient extractants than the corresponding N-acyl(thio)urea derivatives, whereas the latter ones show an interesting selectivity for americium (III) over europium (III) in the presence of Br6-COSAN. The introduction of a propyl chain between the cavitand platform and the chelating groups increases the extraction efficiency of the ionophores (8, 11, and 12). A high selectivity was achieved by N-acylthiourea cavitand 12 at pH 3 using Br6-COSAN as a synergist.