3D Volume plots on non-orthogonal mesh

I have a values on a non-orthogonal grid. Think of the parallelepiped shaped grid. I was under impression that similar to cubic grid, where x, y, z and values are provided as flatten vectors, I should be able to plot x, y, z and values on this grid. But 3D Volume or iso-surface plotting does not work for this grid. I wonder what are other limitation? Can I overcome this simply?