Abstract. In this paper we report on the design and analysis of a multilevel method for the solution of the OrnsteinZernike Equations and related systems of integro-algebraic equations. Our approach is based on an extension of the Atkinson-Brakhage method, with Newton-GMRES used as the coarse mesh solver. We report on several numerical experiments to illustrate the effectiveness of the method.Key words. Multilevel method, Newton-GMRES, Ornstein-Zernike equations, nonlinear equations AMS subject classifications. 65H10, 65N55, 65R20, 65T50, 92E10, 1. Introduction. In this paper we propose a fast multi-level method for the solution of a class of integral equations called the Ornstein-Zernike (OZ) equations, which are useful in calculating probability distributions of matter (atoms) in fluid states [10]. Our approach is faster than a Newton-Krylov approach, such as the one proposed in [2], because the linear solver is only used on a coarse mesh problem.The OZ equations were initially designed to model density fluctuations near the critical point via the equilibrium theory of liquids [8,15]. Since then the range of validity and usefulness has been extended to include the entire fluid range of states. This set of nonlinear coupled integral equations has been derived from the full partition function for atomic systems [20] and while essentially never solved without some approximations has proved a useful tool for understanding liquids at the atomic level for over 50 years. While the OZ equation has two unknowns it is usually closed with another often algebraic relation between the two unknown functions. Two useful approximate closure relations are the Perkus-Yevick equation [16] and the hyper netted chain equation [21]. These equations then provide essentially two equations and two unknowns and when convenient may be substituted into the OZ equation to provide a single nonlinear integral equation for the unknown probability distribution function.The equations, when the physical parameters are reasonably adjusted, have solutions which can be achieved by a variety of techniques [10]. Those methods include Picard iteration with or with out relaxation and basis set (variational) methods. In cases where the physical parameters make the equations stiff, iterative solutions are particularly tedious.The objectives of this paper are to describe an multilevel approach for solving the OZ equations and apply that new approach to two examples. The multilevel method is based on the enhanced version of the Atkinson-Brakhage [1, 3] method from [13]. We show that we can compute