The yield of 1- and 2-butyl nitrates in The gas-phase reactions of NO with n-C4H9O2 and sec-C4H9O2 , obtained from the reaction of F atoms with n-butane in the presence of O-2, was determined over the pressure range of 100-600 Torr at 298 K using a high pressure turbulent flow reactor Coupled with a chemical ionization quadrupole mass spectrometer. The yield Of butyl nitrates Was found to increase linearly with pressure from about 3% at 100 Torr to about 8% at 600 Torr. The results obtained are compared With the available data concerning nitrate formation from NO reaction with other small alkylperoxy radicals. These results are also discussed through the topology of the lowest potential energy surface mainly obtained from DFT(B3LYP/aug-cc-pVDZ) calculations of the RO2 + NO reaction paths. The formation of alkyl nitrates, due essentially to collision processes, is analyzed through a model that points out the pertinent physical parameters of this system.