Superpressure balloons were flown in 2002 and 2005 in the winter polar vortices of both hemispheres. The balloons can drift for months in the stratosphere acting as quasi-Lagrangian tracers of air-parcel motions. The meteorological datasets acquired are used to retrieve small-scale internal atmospheric gravity wave parameters using wavelet techniques. For the first time, gravity wave momentum fluxes are estimated over wide geographical areas and the results will help constrain gravity wave parameterization schemes used in general circulation climate models. The importance of mountain waves is confirmed, with largest fluxes observed in the lee of Greenland and the Antarctic Peninsula. However, significant momentum fluxes are also observed over the oceans, showing the importance of other wave generation mechanisms.