Bubble characteristics such as shape, size, number and motion control the hydrodynamics and therefore heat transfer and chemical conversion in fluidized bed reactors. Thus understanding these characteristics is very important for the design and scale-up of fluidized beds. In this work a digital image analysis technique was developed to study the bubble behavior of two-dimensional bubbling beds with and without immersed horizontal tubes. Digital image analysis is a non-intrusive measurement technique which can simultaneously provide a great quantity of information without interfering with flow dynamics. The technique developed and implemented in this study allowed for the simultaneous measurement of various bubble properties, such as bubble diameter, rise velocity, aspect ratio and shape factor. A robust in-house code was developed to fully automate the image acquisition and data processing procedure. The experimental results obtained were validated and found to be in good agreement with available literature correlations. Moreover, based on the experimental results obtained new correlations for bubble growth and rise velocity as a function of bed height above the distributor were proposed. The models were in good agreement with the experimental data for a wide range of superficial velocities and particle sizes. (C) 2011 Elsevier B.V. All rights reserved.