  Ultraluminous X-ray sources are non-nuclear point sources exceeding the
Eddington luminosity of a 10 Solar mass black hole. Modern consensus for a
majority of the ULX population is that they are powered by stellar-mass black
holes or neutron stars accreting well above the Eddington limit. Theoretical
models of super-Eddington accretion predict existence of powerful outflows of
moderately ionised gas at mildly relativistic velocities. So far, these winds
have been found in 3 systems: NGC 1313 X-1, NGC 5408 X-1, NGC 55 ULX. In this
work, we create a sample of all ULXs with usable archival high resolution X-ray
data, with 10 sources in total, in which we aim to find more signatures of
outflows. We perform Gaussian line scans to find any narrow spectral
signatures, and physical wind model scans where possible. We tentatively
identify an outflow in NGC 5204 X-1, blueshifted to 0.34c, which produces
emission features with a total significance of at least 3$\sigma$. Next we
compare ULXs with similar hardness ratios. Holmberg IX X-1 shows absorption
features which could be associated with a photoionized outflowing absorber,
similar to that seen in NGC 1313 X-1. The spectrum of Holmberg II X-1 possesses
features similar to NGC 5408 X-1 and NGC 6946 X-1 shows O VIII rest-frame
emission. All other sources from the sample also show tentative evidence of
spectral features in their high resolution spectra. Further observations with
the XMM-Newton and Chandra gratings will place stronger constraints. Future
missions like XARM and Athena will be able to detect them at larger distances
and increase our sample.
