A wide range of combinations of gas and liquid flow rates that form various flow patterns are investigated. By analyzing the signal spectra detected by a single sensor using light techniques, the criteria for identifying two-phase flow patterns are proposed. By applying these criteria with only one parameter, the high-frequency contribution fraction (HFCF), the reasonable identifying performance is 76% when churn flow is counted and 88% when churn flow is not counted. When ᾱ is added as an auxiliary to HFCF, the identifying performance can be increased to 83 and 96%, depending on whether churn flow is counted. Both parameters can be acquired by signals from a single void fraction sensor. The criteria are expected to apply to other void fraction measurable systems for identifying two-phase flow patterns.