There are many parameters in tillage operations that affect the fuel consumption of a tractor. Also there are several methods for measuring tractor fuel consumption. In this study tractor fuel consumption was measured by flowmeter sensors. The measurement system was installed on the engine of a 72.3 KW John Deer 3140 tractor because it is one of the useful tractors, with long service life and high efficiency in Iran. A three-share disc plough was used for studying the effect of plough depth variations on tractor fuel consumption. Results showed that the tractor with the disc plough attached at depths of 15, 23 and 30 cm consumed 19.667, 24.715 and 28.646 l of fuel per hectare, respectively. Increasing plough depth from 15 to 23 and 23 to 30 cm increased fuel consumption by 25 and 15.9%, respectively. The average fuel consumption was 24 l ha-1 at the common plough depth of 15 to 30 cm. Instantaneous fuel consumption during operation of mouldboard plough at three depths increased when working depth increased. In farm experiments, only the working depth of plough was changed, but variations in time-consumption diagram showed that there are other factors affecting draft and thereby fuel consumption during operation, although depth variations had a more pronounced effect than others on fuel consumption.