Ammonia (NH 3 ) and hydrogen sulfide (H 2 S) are emitted from beef cattle feedlots with NH 3 being greater by nearly three orders of magnitude. Nearly 30% of the U.S. beef cattle are fed in the High Plains of Texas. Earlier research indicates that abatement technologies may be needed to significantly reduce NH 3 emissions. To date, little is known about the appropriate measurement methods to evaluate the effectiveness of NH 3 emission controls. In this research, we determined the (a) variability of NH 3 and H 2 S fluxes within a single pen and (b) the relationships between NH 3 and H 2 S fluxes and manure characteristics as a part of a larger field study to determine the effectiveness of the urease inhibitor NBPT. A dynamic, flow-through chamber system was used to estimate NH 3 flux from experimental beef cattle pen with a 15.6 m 2 /head stocking density. The total of 27 measurements were completed within one day using a flux chamber interfaced with an on-site, mobile-instrument shelter. Manure samples from each location were analyzed for moisture content, total kjeldahl nitrogen (TKN), NH 4 -N, NO 3 -N, and C:N to characterize their relations with NH 3 -N and H 2 S-S flux. The NH 3 -N flux varied by nearly 30 fold between 512 to 14,993 µ g/m 2 -min. The H 2 S-S flux varied from 0.52 to 8.07 µ g/m 2 -min. In addition, flux from fresh urine and feces were also measured for nearly one day. The cumulative NH 3 -N emissions from fresh feces were 2.5 to 13.7% of NH 3 -N from urine. The apparent variation of flux within a typical pen has important implications on the selection of appropriate measurement methods for statistically significant evaluation of emission controls.