Steady-state four-level microwave double-resonance experiments are described for pure OCS and OCS diluted with CH 3OH, H 2, and He. For pure OCS, interactions of higher order than first-order dipole-dipole dominate the behavior of some four-level systems, and the rates of Δ J = 2 quadrupole-type collision-induced transitions are found to be greater than one-half of the Δ J = 1 dipolar rates. For OCSCH 3OH mixtures, the dipolar rates are significantly enhanced with respect to the pure gas, but Δ J = 2 transitions are still important. For the mixtures of astrophysical interest, OCSH 2 and OCSHe, all four-level systems show Δ J = 2 collisional preferences. The Δ J = 2 transition rates are comparable to those of Δ J = 1 transitions, and there is evidence that Δ J = 3 transition rates are substantial.