The relative agronomic effectiveness (RAE) and relative economic effectiveness (REE) of Christmas Island phosphate rock (CIPR) and Gafsa phosphate rock (GPR), compared to triple superphosphate (TSP), were evaluated in five acid Malaysian soils (pHw 4.45-5.0) in a greenhouse experiment using the tropical grass Setaria splendida L. as the test crop. There were significant differences between soils in the total dry matter (DM) yield of Setaria in 10 harvests spreading over a 20-month period. The DM yield of Setaria decreased in the following sequence: Kundor > Segamat > Bungor > Tok Yong > Durian soils. The response of Setaria to the P treatments was clearly indicated by the DM yield and for each soil TSP was superior to either CIPR or GPR. The RAE of GPR (90%) was higher than that of CIPR (72%). However, for the long-term supply of P, both CIPR and GPR were much more cost-effective than TSP, with REE values of 131 and 143% for CIPR and GPR, respectively.