  We analyse the problem of singularity of graphs for hexagonal grid graphs. We
introduce methods for transforming weighted graph, which do not change the
determinant of adjacency matrix. We use these methods to calculate the
determinant of all hexagonal grid graphs which describe certain hexagon-shaped
benzenoid systems. The final result is the explicit formula for the determinant
of graphs $H_{k,n}$. From the theorem we draw the conclusion, that all graphs
of this kind are non-singular.
