Methods and apparatus for ranking uncertain data in a probabilistic database are disclosed. An example method disclosed herein comprises using a set of data tuples representing a plurality of possible data set instantiations associated with a respective plurality of instantiation probabilities to store non-deterministic data in a database, each data tuple corresponding to a set of possible data tuple instantiations, each data set instantiation realizable by selecting a respective data tuple instantiation for at least some of the data tuples, the method further comprising determining an expected rank for each data tuple included in at least a subset of the set of data tuples, the expected rank for a particular data tuple representing a combination of weighted component ranks of the particular data tuple, each component rank representing a ranking of the data tuple in a corresponding data set instantiation, each component ranking weighted by a respective instantiation probability.