where a(p) = 3(2/p 1) and the constant C depends on the L2 and Lnorms of the initial data u0. This paper deals with the more subtle problem of deriving lower bounds on the energy decay rates. We show that for a certain class of initial data the solutions u(x, t) to the 2D and 3D Navier-Stokes equations admit an algebraic lower bound on the energy decay. Specifically, there are two cases to consider. In the first case, the average of the initial data f u0 dx is nonzero. This case was treated in the earlier paper [5] where it was established that