Techniques for a maximum entropy approach to assigning probabilities, including those used in multiple realization history matching systems and methods, are disclosed. For example, in one embodiment, a method includes obtaining one or more available sample values Yi associated with a reservoir; computing a maximum entropy assignment λ of one or more discrete probabilities Pi(Yi) associated with each of the one or more available sample values Yi, where each discrete probability Pi(Yi) represents a probability that one or more variables Y will take a set of particular values Yi; and performing at least one determination regarding the reservoir using the maximum entropy assignment λ, including approximating a continuous probability distribution P(Y) using a sum of probability distributions Pi(Yi)+/−λ.