The data available in the literature for the excess Gibbs energies GE, excess enthalpies HE, activity coefficients γ∞i, and partial molar excess enthalpies hE,∞i at infinite dilution, and excess heat capacities CEP of noncyclic monoethers, polyethers, acetals and orthoesters and of cyclic monoethers + n-alkanes or + cyclohexane are examined on the basis of the DISQUAC group contribution model. The interaction parameters, quasichemical and dispersive, depend on the intramolecular environment of the O atom. There is clear evidence for a steric effect exerted by the alkyl groups adjacent to the O atom, for OCO proximity effect (in acetals and orthoesters), and for a ring strain effect (in cyclic ethers). The steric effect results in a regular decrease of the quasi-chemical interaction parameters; the dispersive parameters remain constant. The proximity effect of O atoms produces a regular decrease, and the ring strain a regular increase, in both the quasi-chemical and the dispersive interaction parameters.