The permanent electric dipole moments of the ground, and the low-lying excited electronic states of platinum monocarbide, PtC, platinum monoxide, PtO, and platinum monosulfide, PtS, were measured using a molecular beam optical Stark spectroscopic scheme. The determined values were (in Debye) : PtO(X (3) Sigma(-)) 2.77(2); PtO(A (1) Sigma(+)) 1.15(4); PtS[X(Omega=0)] 1.78(2); Pts[B(Omega=0)] 0.54(6); PtC(X (1) Sigma(+)) 0.99(5); and PtC(A (1) Pi) 2.454(3). These results, along with the previous results for PtN(X (2) Pi(1/2)> 1.977(9); PtN(d (4) Pi(1/2)> 1.05(9) [J. Chem. Phys. 102, 643 (1995)], are used as a basis for a discussion of the nature of the electronic states.