We present a search for a standard model Higgs boson produced in association with a W boson using 2.7  fb−1 of integrated luminosity of pp collision data taken at s√=1.96  TeV. Limits on the Higgs boson production rate are obtained for masses between 100 and 150  GeV/c2. Through the use of multivariate techniques, the analysis achieves an observed (expected) 95% confidence level upper limit of 5.6 (4.8) times the theoretically expected production cross section for a standard model Higgs boson with a mass of 115  GeV/c2.