N-(n-Butyl)thiophosphoric triamide (NBPT) has been reported to reduce ammonia volatilization from surface-applied urea and urea ammonium nitrate (UAN). A new NBPT formulation (ARM U^™, 18% NBPT) that contains a polymer allowing for lower application rate of NBPT was evaluated for its efficacy relative to Agrotain^® (30% NBPT) and Arborite^® (24% NBPT). Trials consisted of (i) a greenhouse study that compared two rates of ARM U-treated urea (360 and 540 mg NBPT kg^-1 urea) with Arborite- or Agrotain-treated urea (480 and 600 mg NBPT kg^-1 urea, respectively) and (ii) a field study that compared urea and UAN treated with either ARM U (360 mg NBPT kg^-1 urea) or Agrotain (600 mg NBPT kg^-1 urea) at two sites. Static chambers fitted with acid-charged discs were used to measure ammonia volatilization at six or seven dates over 28 d. In the greenhouse study, ammonia volatilization was reduced by 96% with either ARM U or Agrotain and 95% with Arborite. In the field study, ARM U and Agrotain reduced ammonia volatilization from urea by 80% and 66%, respectively, across sites. Similarly, ammonia volatilization from UAN was reduced by 46% and 60% with ARM U and Agrotain, respectively. Despite the lower NBPT application rates with ARM U, ammonia reduction by ARM U, Agrotain, and Arborite was not significantly different. The addition of ARM U to urea and UAN enabled lower application rate of NBPT without compromising its efficacy.