Studies dealing with the market power of a firm depend on the elasticity of demand even when market imperfection is acknowledged. This study suggests that a firm derives its market power due to its interface with consumers on the market as well as its interaction with rival firms on the market. As a result, its market share and market power over a unit of sales in the industry require attention in the context of imperfect markets. Similarly, non-price strategies of firms offer some market power that should be incorporated in the definition. Thus the modified market power indices are a significant contribution to the theoretical results.