1. A production simulator, for simulating a mature hydrocarbon field, providing quantifies produced per phase, per well, per layer or group of layers and per time as a function of production parameters, wherein said production simulator is defined by a set of parameters α within a space of solutions, matches history data of said mature hydrocarbon field and exhibits a good forecast reliability, which can be characterized, according to the Statistical Learning Theory, by low forecast expected risk R(α) associated with said parameters α .