  We study the energy-momentum tensor of stable, meta-stable and unstable
Q-balls in scalar field theories with U(1) symmetry. We calculate properties
such as charge, mass, mean square radii and the constant d1 ("D-term") as
functions of the phase space angular velocity omega. We discuss the limits when
omega approaches the boundaries of the region in which solutions exist, and
derive analytical results for the quantities in these limits. The central
result of this work is the rigorous proof that d1 is strictly negative for all
finite energy solutions in the Q-ball system. We also show that for Q-balls
stability is a sufficient, but not necessary, condition for d1 to be negative.
