Fuel economy of tractor diesel engines of low, moderate, and high nominal (rated) power is analyzed using the engines regulator characteristics. The method for constructing the generalized regulator characteristic has been developed. Analytical correlations between brake specific fuel consumption (BSFC) and brake power of the engine are obtained under restriction of fixed allowed error. Fuel economy of the engines of different nominal power is analyzed. Dimensionless regulator characteristics are used for generalization of the results of analysis.Engine performance characteristics, viz, nominal BSFC and estimated BSFC, have been calculated. A new general characteristic of the fuel consumption - estimated operational BSFC is introduced. It accounts for fuel consumption of the engine operating in a wide range of loads and speeds. Admissible ratios between rated, estimated, and estimated operational BSFC-s have been determined for diesel engines of various power.