We introduce an electrostatic model including charge transfer, which is shown to account for the observed B-site ordering in Pb-based perovskite alloys. The model allows charge transfer between A sites and is a generalization of Bellaiche and Vanderbilt’s purely electrostatic model. The large covalency ofPb2−compared toBa2+results in an environment dependent effective A-site charge. This model successfully reproduces the long range order of both Pb-based and Ba-based complex perovskite alloys. It yields smaller structural energy differences for Pb-based compared to Ba-basedA(B1/3B2.3)O3systems, consistent with first-principles calculations and the fact that Ba-based disorder at higher temperatures than the Pb-based alloys. ©2000 American Institute of Physics.