Let W be a real-valued, two-parameter Brownian sheet. Let us define N(
t; h) to be the total number of bubbles of W in [0, t](2), whose maxim
um height is greater than h. Evidently, lim(h down arrow 0) N(t; h) =
infinity and lim(t) (up arrow) (infinity) N(t; h) = infinity. It is th
e goal of this paper to provide fairly accurate estimates on N(t; h) b
oth as t --> infinity and as h --> 0. Loosely speaking, we show that t
here are of order h(-3) many such bubbles as h down arrow 0 and t(3) m
any, as t up arrow infinity.