The numeraire portfolio (defined as the admissible self-admissing strategy such that relative prices are martingales in the historical probability) is unique under complete as well as incomplete markets. We use the portfolio attributes of this numeraire portfolio to identify the prices of new redundant or non redundant securities added to incomplete markets. We characterize the equilibrium price, using the minimax local martingale introduced by the He-Pearson.
BAJEUX-BESNAINOU, I. and PORTAIT, R. (1995). Pricing Contingent Claims in Incomplete Markets Using the Numeraire Portfolio. In: Journées Internationales de Finance. Université de Bordeaux, pp. 1-25.