Improved estimates of bubble dynamics in industrial gas-liquid fluid systems are important for accurately modeling multiphase flow. In many gas-liquid industrial systems at elevated pressure, bubbles exist in a polydisperse size population. This work experimentally characterizes the effects of bubble swarm polydispersity and gas holdup on drag using a monofibre optical probe in an ethanol contaminated aqueous system, providing an evaluation of current swarm drag models under industrially relevant pressures and high gas holdup conditions (up to 37% gas fraction). At atmospheric pressure, the rise velocity and swarm-corrected drag of individual bubbles within a polydisperse distribution of bubbles was found to be well-predicted by the swarm correction model of Lockett and Kirkpatrick (1975). An improved fit to the reported data was found using a piecewise isolated single bubble drag coefficient correlation. At elevated pressures (6.5 MPa), swarm hindrance effects were not observed for detected bubbles and the rise velocity and drag coefficient of individual bubbles within a polydisperse distribution were well predicted without the use of a swarm correction model. (C) 2016 Elsevier Ltd. All rights reserved.