Simulations are presented of 94-GHz and 9-GHz EPR spectra from phospholipid probes spin-labeled at the C4 to C14 positions of the sn-2 chain in liquid-ordered membranes of dimyristoyl phosphatidylcholine that contain 40 mol % cholesterol. Spectra at 94 GHz can be simulated adequately by motional narrowing theory. The latter accounts better for averaging of the g(xx)/g(yy) canonical features, with a restricted rotation about the z axis, than do slow-motional descriptions (Brownian and strong-jump) of unrestricted phi rotation. Polarity-corrected g tensors are required for the high-field simulations. These are obtained from measurements at low temperature (-100 degreesC) by comparing the polarity profile with spin-label position, n, that is based on g(0) (i.e., the trace of the g tensor) with that established from simulations of experimental spectra at the measurement temperature of +30 degreesC. Model simulations for Brownian rotational diffusion indicate that the A(zz) element of the N-14 hyperfine splitting of the 94-GHz spectra is relatively insensitive to slow off-axial diffusion. This result is used to derive spin Hamiltonian tensors that are partially averaged by the fast motional component, from the high-field spectra. These are then used in the stochastic Liouville equation to obtain anisotropic parameters of the slow motional component that is evident in the experimental 9-GHz spectra. The rapid diffusional component is attributed to segmental motion of the lipid chains, and the slow diffusional component to angular fluctuations of the chain axis. The latter are not constant throughout the length of the chain, but increase in intensity towards the terminal methyl region.