A new methodology is applied to ERA40 reanalysis in order to quantify large-scale inertia-gravity wave activity in the equatorial lower stratosphere. Both eastward and westward propagating waves are identified in the data set and a good agreement is found with previously published in situ observations. Global estimates of vertical fluxes of zonal momentum associated with such waves are obtained. Typical amplitudes of order 10-2 m2. s-2 suggest that the forcing of the Quasi-Biennial Oscillation by large-scale inertia-gravity waves is tantamount to that by Kelvin waves. This method can be used to document the space-time variability of the wave-activity in order to improve the wave-drag parameterizations in climate models.