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We demonstrate an application of least-squares wave-equation inversion using time-lapse data sets from the Valhall field. We pose time-lapse imaging as a joint least-squares problem that utilizes target-oriented approximations to the Hessian of the objective function. Because this method accounts for illumination mismatches--caused by differences in acquisition geometries--and for band-limited wave-propagation effects, it provides better estimates of production-related changes in reservoir acoustic properties than conventional time-lapse processing methods. We show that our method improves image resolution (compared to migration) and that it attenuates obstruction artifacts in time-lapse images.