A large body of literature is available in the field of bubble column reactors, focusing mainly on hydrodynamics. However, the mixing pattern, extent of back-mixing, and effect of scale on mixing are not well investigated, especially for large size columns, partly because tracer experimental measurements in large-scale columns are difficult. This can be alleviated by computational experiments. This study focuses on using a virtual tracer experiment coupled with a two-phase three-dimensional computational fluid dynamics (CFD) simulation to investigate mixing characteristics in large reactors. The results are validated by comparison with experiments. Both gas-and liquid-phase mixing patterns are reported in terms of dispersion coefficient and mixing time, and information is provided for the diameter range 0.14-0.90 m and for various height/diameter ratios. Empirical the scale effect on dispersion coefficient are provided. The results are useful in the context of dispersion-based phenomenological models for bubble columns, especially for multiple reactions with a large spread in the reaction time values.