Empirical models of the two largest constituents of the long-period ocean tides, the monthly and the fortnightly constituents, are estimated from repeat cycles 10 to 210 of the TOPEX/POSEIDON (T/P) mission. These models are first validated with tide gauge observations which show residual variances with the T/P-derived models that are of the order of 2--3 mm2 for both the monthly and fortnightly constituents, and which are smaller than residual variances from respective equilibrium models of these long-period ocean tides. These empirical models are used to predict the contribution that they each have on tidal variations of the Earth's rotation rate. For tidal variations in UT1 these contributions are predicted to be of the order of 0.1 ms with a scatter of the order of 8 and 3 &mgr;s for the monthly and fortnightly ocean tides, respectively. ¿ 1999 American Geophysical Union