In the Current Work, Nuclear Gauge Densitometry (NGD), Which is Commercially Available and Industrially Used for Liquid/slurry Level Measurement and Control, Has Been Employed to Identify Fingerprints of the Prevailing Hydrodynamic Flow Regime. Experiments Were Performed using an Air-Water System in 0.1012. M Diameter and 1.2. M Long Bubble Column at Ambient Pressure. the Superficial Gas Velocities Were Varied from 1. Cm/s to 12. Cm/s with an Interval of 0.5. Cm/s Near Transition Region. the Flow Regime Boundaries Were Defined using the Conventional Methods of Flow Regime Demarcation Such as the Change in the Slope of the overall Gas Holdup and the Drift Flux Plot. the Obtained Photon Counts History Was Subjected to Various Time-Series Analyses. based on the Comparison with the Results of Conventional Methods, Objective Flow Regime Identifiers for NGD Were Proposed. the Obtained Flow Regime Identifiers Can Be Helpful for Online Flow Regime Monitoring in Laboratory as Well as Industrial Bubble Column Reactors. © 2012 Elsevier Ltd.