The forces between layers of poly(ethylene oxide) (PEO), of molecular weights M = 37 × 103 (PEO37) and M = 112 × 103 (PEO112) adsorbed onto smooth, curved solid (mica) surfaces across the good solvent toluene have been determined using a surface force balance (SFB). The SFB used is capable of measuring both normal interactions Fn(D) as a function of surface separation D and, with extreme sensitivity, shear or frictional forces Fs(D,νs) between them as they slide past each other at velocity νs. The Fn(D) profiles are closely similar to those measured in earlier studies between adsorbed PEO layers. The shear or frictional forces between the sliding PEO-bearing surfaces are very low up to moderate compressions of the adsorbed layers (local pressures up to ca. 105 N m-2), corresponding to effective friction coefficients μeff = (Fs/Fn) of order 0.003 or less. This is attributed to the fluid interfacial layer between the adsorbed layers resulting from their weak mutual interpenetration. At higher loads Fs increases markedly, and two forms of behavior are found depending on the PEO molecular weight. For PEO37, a sharp increase in Fs is followed by removal of polymer from within the intersurface gap during sliding, high friction, and adhesion between the surfaces. For the longer PEO112, the initial increase in Fs and in μeff saturates at the highest loads (for the case of μeff even decreasing), indicating that the slip plane has moved from the polymer/polymer midplane to the polymer/ solid interface. The dependence of Fs on the sliding velocity in the high-friction regime is weak, suggesting that at low compressions there is a thinning of the mutual adsorbed-layer-interpenetration region at high νs that offsets the higher viscous dissipation in that region. At the highest loads, when the slip plane has shifted to the mica surface, the weak Fs(νs) dependence is characteristic of sliding friction at solid substrates.