  We explore constraints on the Milky Way dark matter halo oblateness using
three stellar streams from globular clusters NGC 3201, M68, and Palomar 5.
Previous constraints on the gravitational potential from dynamical equilibrium
of stellar populations and distant Milky Way satellites are included. We model
the dark halo as axisymmetric with axis ratio $q_\rho^{\rm h}$ and four
additional free parameters of a two power-law density profile. The halo axis
ratio, while barely constrained by the NGC 3201 stream alone, is required to be
close to spherical by the streams of Palomar 5 ($q_\rho^{\rm h}=1.01\pm0.09$)
and M68 ($q_\rho^{\rm h}=1.14^{+0.21}_{-0.14}$), the latter allowing a more
prolate shape. The three streams together are well fitted with a halo axis
ratio $q_\rho^{\rm h}=1.06\pm0.06$ and core radius $\sim$ 20 kpc. Our estimate
of the halo shape agrees with previous studies using other observational data
and is in tension with cosmological simulations predicting that most spiral
galaxies have oblate dark matter halos with the short axis perpendicular to the
disc. We discuss why the impact of the Magellanic Clouds tide is too small to
change our conclusion on the halo axis ratio. We note that dynamical
equilibrium of a spherical halo in the oblate disk potential implies an
anisotropic dark matter velocity dispersion, larger along the vertical
direction than the horizontal ones, which should relate to the assembly history
of the Milky Way.
