Many studies have examined the effects of agriculture tractor engine energy performance. This paper presents an evaluation method of such engine actual power use during plowing operations. It includes results of a comparative study of power performance of a 230 kW tractor model John Deere 8330 subject to soil plowing operations as a function of field size: A (26 ha), B (12.74 ha), C (3.22 ha). Statistical data clustering, a relatively novel approach in studies on actual utilization of engine power, was used. A positive correlation was observed between field size and the active state of the engine: 75.2% field A; 68.8% field B; 46.8% field C. The actual power utilization of agriculture tractor engine as a function of field size was 0.62, 0.58 and 0.39 respectively for the three fields used in this study. With this evaluation approach, performance indexes of operational power performance in various conditions were obtained for possible use in optimization of plowing operations.