The article develops an uncertainty analysis for a newly measured variable of local entropy production. Entropy production is measured with post-processing and spatial differencing of measured velocities from particle image velocimetry (PIV), as well as temperatures obtained from planar laser induced fluorescence (PLIF). Measurement uncertainties of fluid velocity depend on the time interval between laser pulses, width of the camera view and other factors. Bias errors are related to elementary bias components and sensitivity coefficients in the uncertainty analysis. The precision errors use a confidence coefficient of 2 for a 95% confidence interval. The newly developed measurement technique and uncertainty analysis are successfully applied to pressure-driven channel flow and buoyancy-driven free convection in a square enclosure. (c) 2004 Elsevier Ltd. All rights reserved.