  Recent measurements of the time-dependent CP asymmetry of the B -> phi K_S
decay give results whose central values differ from standard model
expectations. It is shown how such data can be used to identify new physics
contributions in a model-independent manner. In general, a sizeable new
amplitude with nontrivial weak and strong phases would be required to explain
current data. Improvement in the quality of data will allow one to form a more
definite conclusion.
