If radiocarbon were a good predictor of the amount of time until a water parcel returns to the surface, it could be used to estimate the effectiveness of carbon sequestration by direct injection. We performed direct CO2 injection simulations in both one-dimensional box-diffusion and three-dimensional ocean general circulation models. The 1-D model results for ocean carbon retention accord with the 3-D model results, especially in the Pacific basin and at shallower depths. In the 1-D model, carbon retention in the ocean is directly related to both the injection depth and the Δ14C of carbon at the injection location. However, in the 3-D model, depth, but not radiocarbon, provides a relatively good prediction of carbon retention. This suggests that the expected time for a water parcel to return to the surface is closely related to its depth and not in general to the time since last at the surface.