The explanation of persistent excess labor supply is a challenge to macroeconomic theorists. In a purely competitive framework, it may be argued that unemployment is transitory since wages will react if excess supply is persistent enough for the economy to be driven towards full employment. Nevertheless, classical tatonement models do not support this view since excess demand functions are arbitrary, see Shafer and Sonnenschein (1982), and convergence to the Walrasian equilibrium cannot be guaranteed. Fixed-price theory accounts for unemployment at the cost of total indeterminacy of equilibrium allocations. Many efforts have been made in order to narrow down this set. Roughly speaking, these attempts can be classified into two groups: (i) the conjectural approach, cf. Benassy (1976), Negishi (1974), Grandmont and Laroque (1976) and Hahn (1977,1978); (ii) the game theoretical approach, cf. Hart (1982), Madden (1983) and Silvestre (1988). In this paper we want to contribute to the first tine of thinking, by applying the rationality notion developed for a conjectural equilibrium model in Trujillo (1985) to a standard three-goods fixed price model. Both kinds of equilibria are equivalent; see John (1985). The motivation behind our approach is that when agents set prices they have to respect the rules of the mechanism. For instance, in Hahn's rationality approach, agents may change prices even if they are not constrained. However, the assumed mechanism is such that this behavior is not allowed (see below). Therefore agents must be cheating, Le., Hahn's notion is one of incentive compatibility and it is not surprising that he obtained negative results. In our approach, agents may change prices if they are conjecturable in the following sense: if buyers are rationed they can increase conjecture higher prices and if sellers are constrained