By use of a modern BOD bottle probe, a digital read‐out meter, and quadruplicate sampling, oxygen concentrations were routinely measured with a precision of ± 0.02 g DO m−3. This level of accuracy permitted measurement of Water Oxygen Demand (WOD), Net Production (NP), and Gross Production (GP) at all depths in the water column of lakes. Sediment Oxygen Demand (SOD) was also measured and found to be small when compared to the total water column oxygen demand in unstratified water but was a significant part of the hypolimnetic oxygen uptake. Measurements of GP were found to correlate closely with primary production values determined independently by means of the14C technique. Significant GP was also found in the hypolimnion of a mesotrophic lake, indicating that WOD does not always provide a measure of hypolimnetic oxygen uptake; net production does so in this situation. Further, WOD was found to decrease by about 20% per day in incubated samples, revealing that WOD incubations should never exceed one day in duration.