Pure paraffinic hydrocarbons and petroleum fractions (which may be aromatic-free) on vapor phase oxidation give an oxidized product useful as a co-surfactant and as a feedstock for the synthesis of sulfonates. The oxidations may be carried out in a simple tubular reactor using oxygen or air as the oxidant and nitrogen or steam as the reactor diluent and reaction-heat absorber. The reaction is non-catalytic and occurs readily at atmospheric pressure at temperatures ranging from 300 to 400°C. The major products of the oxidations are cyclic ethers mixed with varying proportions of olefins and carbonyls. Mild conditions (low temperatures and the use of diluents) favor the formation of the cyclic ethers and other oxygenated compounds over olefins. The cyclic ethers are largely composed of 5- and 4-membered rings containing carbon and a single oxygen atom. Such products are useful as co-surfactants and as starting material for the manufacture of sulfonates. The oxidized products which are rich in cyclic ethers react readily with sulfur trioxide or oleum to give sulfonates as the principal products. Such sulfonates are effective surfactants in tertiary oil recovery. Low concentration slugs formulated from the above surfactants have performed well in core tests. Highest oil recoveries have been achieved by matching the min of the slug with the EACN of the oil in place. Such matched properties always give slugs having low inter-facial tensions with the oil to be recovered. The sulfonates in low concentration slugs without co-surfactants or viscosity control in the slug have produced oil in core tests at high efficiency levels.