Kentucky bluegrass seed fields in central and southern Oregon, and dryland conditions of eastern Washington use surface applied nitrogen. Fertilizer is generally applied following the conclusion of the irrigation season in mid October and is dependent on natural precipitation for incorporation. Volatile nitrogen loss as ammonia (NH₃) is an economic and environmental concern. The objective of this study was to quantify ammonia volatilization from urea, urea coated with the urease inhibitor (N-(n-butyl) thiophosphoric triamide (NBPT), trade name Agrotain), urea ammonium nitrate (UAN) and CAN 27 applied to the soil surface in the fall under commercial field conditions. During the fall of 2010 the study was conducted at a total of five sites, four irrigated sites two each in central and southern Oregon and a site in the Palouse of eastern Washington. Ammonia volatilization losses were measured with a modified passive flux method, which consisted of a rotating 3 m tall mast placed at the center of each 30 m diameter plot. Ammonia volatilization losses were sampled at five heights using glass tubes coated with oxalic acid. Nitrogen was applied at the rate of 168 kg/ha and monitored over a two-week period. Nitrogen loss due to ammonium volatilization was highest with urea (32-44%) followed by UAN (15-19%). Agrotain-coated urea and CAN 27 produced lower but similar levels (0-14%) of volatilization. Across nitrogen sources the greatest volatilization occurred at the dryland production site in eastern Washington, with less volatilization in central and southern Oregon.