We examine the global stability of an exponential stellar disk embedded in a dark matter halo and constrain the mass-to-light ratio of observed disks in the I-band , \Upsilon _ { I } .
Assuming only that the radial surface density distribution of disks is exponential , we derive an analytic upper limit : \Upsilon _ { I } \la 2.4 h , for a Hubble constant of 100 h~ { } \mbox { km s$ { } ^ { -1 } $ } \mbox { Mpc } ^ { -1 } .
Using N -body simulations we derive a stability criterion significantly different from that of previous authors .
Using this criterion we argue that , almost independent of the concentration of the halo , \Upsilon _ { I } \la 1.9 h .
We discuss this result in relation to other independent determinations of \Upsilon _ { I } , its limitations and its implications for theories of disk formation and barred galaxies .