Intracavity saturation Stark spectra with a CO laser are reported for the ν3 band of OCS. The 137 Stark components measured between 2033 and 2063 cm -1 with an accuracy in the range of 1 MHz have been assigned to ∆ v3 = 1 transitions starting from the following levels: 00 0o, 01 10, 10 00, 02 20, 02 00, 11 10, 03 30, and 12 20. Some complementary measurements on ∆ v2 = 2 transitions, obtained with a CO 2 laser, are also reported. Some Π ← Π and ∆ ← ∆ transitions which do not follow the classical selection rules in l have been discussed in detail. A global analysis has been applied and statistical agreement with all data has been obtained. An important result of this analysis is the first direct determination of the dependence of the electric dipole moment of OCS with the ν3 mode. We have improved by an order of magnitude the deduced value for the equilibrium dipole moment: μe = 0.71450(15) D. The effective dipole moments are calculated for all vibrational states up to 530o cm -1.