The rotational spectra of the van der Waals complex of carbonyl sulfide loosely bound to two helium atoms were investigated using a cavity Fourier transform microwave spectrometer and a microwave-microwave double resonance spectrometer. The lowest rotational transitions of seven isotopomers, namely those containing the (OCS)-O-16-C-12-S-12, (OCS)-O-16-C-12-S-34, (OCS)-O-16-C-13-S-32, (OCS)-O-16-C-12-S-33, (OCS)-O-18-C-13-S-32, (OCS)-O-16-C-13-S-14, and (OCS)-O-17-C-13-S-32 subunits, were studied. Hyperfine structures due to the quadrupolar S-33 and O-17 nuclei were also observed and analyzed. The search for higher J transitions was not successful and possible causes are discussed. Information about the OCS-He-2 cluster inferred from the measurements is presented and discussed.