We present a general framework for constructing and analyzing finite volume methods applied to the mixed formulation of second-order elliptic problems on quadrilateral grids. The control volumes, or covolumes, in the grids overlap. An overlapping finite volume method of this type was first introduced by Russell in [T. F. Russell, Tech. report 3, Reservoir Simulation Research Corp., Tulsa, OK, 1995] and was tested for a variety of problems on rectangular and quadrilateral grids in 758-771], Chou

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... and Kwak reformulated it as their mixed covolume method and proved optimal order error estimates using the covolume methodology from [S. However, their treatment was restricted to the case of diagonal coefficient tensor and rectangular grids since a different approach was needed for the quadrilateral (distorted rectangular) case. In this paper we give a new framework, which can handle not only the rectangular anisotropic case but also the anisotropic and irregular grid cases in which the locally supported test functions are images of the natural unit coordinate vectors under the Piola transformation. Our theory sheds light on how to create new test functions using quadratures and now covers Russell's quadrilateral case.