Many iterative algorithms for the solution of large linear systems may be effectively vectorized if the diagonal of the matrix is surrounded by a large band of zeroes, whose width is called the zero stretch. In this paper, a multicolor numbering technique is suggested for maximizing the zero stretch of irregularly sparse matrices. The technique, which is a generalization of a known multicoloring algorithm for regularly sparse matrices, executes in linear time, and produces a zero stretch approximately equal to n /2σ, where 2σ is the number of colors used in the algorithm. For triangular meshes, it is shown that σ ≤ 3, and that it is possible to obtain σ = 2 by applying a simple backtracking scheme.