The importance of interindividual variability in environmental responses has been little studied, although the available information suggests that, e.g., changes in environmental temperature may be associated with changes in variability. We studied, if exposure to water-soluble fraction (WSF) of crude oil can be associated with changes in interindividual variability in phenotype in Daphnia magna, which reproduces parthenogenetically. By using these clonal organisms, we could exclude the possibility that the observed changes were caused by genetic variability. The results show that the variability of oxygen consumption rate decreased in 48 h 30% WSF-exposed animals as compared to 10% WSF-exposed or control animals without a change in the mean of oxygen consumption rate. The clonal Daphnia magna could also be used to study transgenerational effects without genetic contribution, as the different generations are genetically identical. We observed that the oxygen consumption rates in F1 and F2 generations of unexposed and 10% WSF-exposed Daphnia had decreased from parental F0 generation and were also lower than in offspring of 30% WSF-exposed specimens. The studies did not aim at environmental realism but were designed to show the possibility of variability changes without changes in the mean value of a parameter, and transgenerational effects as a result of environmental contamination.