In the present study, gas phase characteristics of oil-gas-water slug and churn flows in a vertical upward pipe with 20 mm inner diameter (ID) are experimentally investigated. We firstly measure the fluctuating signals of a traversable bi-optical fiber probe at different radial positions. The gas phase flow parameter distributions (local gas velocity, local gas holdup) are obtained and the flow structure is uncovered by calculating the series of gas bubble chord lengths at different radial positions. Additionally, in order to describe the flow structure of slug flow, the relative length of the liquid slug, the profile distributions of gas holdup and bubble size in liquid slug are investigated. To understand the nonlinear dynamic characteristics of slug and churn flows, multi-scale cross entropy (MSCE) algorithm is applied to analyze the signals of a high-resolution half-ring conductance sensor and bi-optical fiber probe. The result indicates that multi-scale cross entropy can be an effective tool for validating the measurement of gas phase characteristics by using the traversable bi-optical fiber probe. (C) 2017 Elsevier Ltd. All rights reserved.