Abstract. We give necessary and sufficient conditions for the existence of weak solutions to the model equationin the case 0 < q < p − 1, where σ ≥ 0 is an arbitrary locally integrable function, or measure, and ∆pu = div(∇u|∇u| p−2 ) is the p-Laplacian. Sharp global pointwise estimates and regularity properties of solutions are obtained as well. As a consequence, we characterize the solvability of the equationwhere b > 0. These results are new even in the classical case p = 2. Our approach is based on the use of special nonlinear potentials of Wolff type adapted for "sublinear" problems, and related integral inequalities. It allows us to treat simultaneously several problems of this type, such as equations with general quasilinear operators div A(x, ∇u), fractional Laplacians (−∆) α , or fully nonlinear k-Hessian operators.