We investigate the consumption of a dissolved chemoeffector by bacteria, in a flow generated by buoyancy driven rise of oil drops. Our aim is to quantify the differences in the rate of consumption by motile and non-motile bacteria. We employ direct numerical simulations to resolve the multiphase flow, chemoeffector transport, and bacteria transport in a swarm of rising oil drops. Our simulations indicate that chemotaxis enables motile bacteria to consume the chemoeffector at rates that can be as high as approximate to 45% faster than their non-motile counterparts. We find that the chemotactic advantage depends most acutely on the bacteria's swimming speed, and on their sensitivity toward gradients in chemoeffector concentration. Furthermore, our results reveal that chemotactic advantage reduces monotonically with an increase in the diameter of the drops, while it varies non-trivially with the volume fraction of the drops. (C) 2018 Elsevier Ltd. All rights reserved.