A variation of the simulated-moving-bed (SMB) operation, called Enriched Extract SMB (EE-SMB), is investigated, in which a portion of the extract product is concentrated and the resulting enriched stream is re-injected into the SMB at that same point, i.e., at the inlet of section 2. This operation has been recently patented. [Bailly et al., U. S. Patent Application No. WO2004039468, 2004.] Equilibrium Theory is used (i) to obtain the constraints on the operating parameters and (ii) to identify the operating regimes for the EESMB operation. This analysis is performed for a binary mixture whose adsorption behavior is described by a Langmuir isotherm. The operating regimes are translated into regions on the (m(2), m(3)) plane representation, which can be easily compared with the corresponding operating regimes of the standard SMB given by the Triangle Theory. In particular, for the EE-SMB operation, the region of complete separation turns out to be a line segment, i.e., a one-dimensional locus. The theoretical findings are confirmed through detailed simulations of the process, and the value of the new EE-SMB operation mode is assessed.