Solvent vehicles and methods of their use in the pulse jet delivery of reagents in automated oligonucleotide synthesis by the solid-phase phosphoramidite method are provided. For pulse jet delivery of the activated monomer, acetonitrile in combination with at least one stabilizer co-solvent is employed as the solvent vehicle, where the stabilizer co-solvent is an inert, organic solvent having a boiling point of at least 100.degree. C. For pulse jet delivery of the detritylation reagent, a mono- or disubstituted methane is employed as the solvent vehicle, where substituents have a molecular weight greater than 36 daltons. Use of the solvent vehicles according to the subject invention provides for reduced reagent precipitation in the pulse jet tubes and improved results.