The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. A potential energy surface for He-OCS that agrees with experimental rotational spectra to within 1 MHz is presented. The potential was first calculated at a grid defined in prolate spheroidal coordinates, which give stabler interpolations than Jacobi coordinates. Coupled cluster calculations at the CCSD͑T͒ level were carried out with an aug-cc-pVTZ basis set. The potential was then morphed, a procedure that scales the energy and the intermolecular distance in a coordinate-dependent way. The parameters of the function used for morphing were determined by a least-squares fit to the experimental data. The global minimum of the recommended potential, at Ϫ50.2 cm Ϫ1 , is 4.8 cm Ϫ1 deeper than the unscaled potential of Higgins and Klemperer ͓J. Chem. Phys. 110, 1383 ͑1999͔͒. The morphing procedure increases the well depth by more at the sulfur end than at the oxygen end.