We present some exact results for mixtures of nonadditive hard spheres and use them to derive two models for the contact values of the pair correlation functions and the equation of state. The new models are general in that they are not limited to binary mixtures, equal size components, or a certain range of the nonadditivity parameter. Comparison with the available computer simulation data for equal size components show that the new models predict satisfactory the equation of state data and the contact values. The prediction of the critical point of fluid-fluid phase separation is satisfactory at small and large values of the nonadditivity parameter, and less so at intermediate values.