In this paper we further explore a class of high order TVD (total vari
ation diminishing) Runge-Kutta time discretization initialized in a pa
per by Shu and Osher, suitable for solving hyperbolic conservation law
s with stable spatial discretizations. We illustrate with numerical ex
amples that non-TVD but linearly stable Runge-Kutta time discretizatio
n can generate oscillations even for TVD (total variation diminishing)
spatial discretization, verifying the claim that TVD Runge-Kutta meth
ods are important for such applications. We then explore the issue of
optimal TVD Runge-Kutta methods ibr second, third and fourth order, an
d for low storage Runge-Kutta methods.