In the article some aspects of the market value of lignite reserves have been analysed. It has been defined the range of application to fix this value using recommended NPV method, e.g. to project exploitation od perspective deposits. The author presents the method to evaluate proved mineral reserves, considering economical criteria by means of newly created parameter. Employing this method fulfils the condition of rational reserves administration. The results have been compared to the data taken from mining projects and economical analysis of new deposits. Other applications of the method have also been suggested, e.g. for projections of exploitation as a function of income rather than a function of production, especially as a way of estimate the profits of prospective lignite deposits which constitute a base for future power industry. This verification should also provide for the use of the simplified NPV method.