The period of Density Wave Oscillations (DWOs) in an uniformly heated horizontal test section is experimentally investigated. The test section consists of a 5 mm I.D. pipe where R134a is used as working fluid. The experiment is performed for a range of inlet pressures P-i [500-1200 kPa], inlet sub-cooling [10 and 20-K], maintaining constant heat fluxes q" [38 kW/m(2)] and mass flux G [300 kg/m(2)s]. The effect of the system parameters on the period of the DWOs is studied. It is observed that the period of the DWOs increases as inlet pressure and inlet sub-cooling temperature increase. Furthermore it is observed changes in the period which might be connected to the changes in the flow regime distribution inside the pipe. (C) 2015 Elsevier Ltd. All rights reserved.