Economic operation is a major concern for microgrids (MGs). System operation cost is optimized when the incremental costs (ICs) of all distributed generators (DGs) reach equality. Conventionally, economic dispatch of DGs is solved by centralized control with optimization algorithms or distributed control with consensus algorithms. To improve the reliability, scalability, and economy of MGs, a fully decentralized economic power sharing strategy is proposed in this paper. As frequency is a global state in ac MG and dc bus voltage serves as a natural indicator in dc MG, a frequency-IC droop scheme is proposed for ac MG, a voltage-IC droop scheme is proposed for dc MG, and a normalization scheme is proposed for hybrid ac/dc MG. By using the proposed technique, ICs of DGs reach equality with the convergence of the system global indicator (frequency or dc bus voltage). Then power sharing of each DG is automatically achieved based on its relevant IC function and the total operating cost can be optimized without any communication or central controllers. The proposed approach is implemented in an ac MG, a dc MG, and a hybrid ac/dc MG in MATLAB/Simulink to verify its effectiveness.