Concentrations of CH4, a potent greenhouse gas, have been increasing in the atmosphere at the rate of 1 ~ per year. The objective of these laboratory studies was to measure the effect of different forms of inorganic N and various N-transformation inhibitors on CH 4 oxidation in soil. NH~ oxidation was also measured in the presence of the inhibitors to determine whether they had differential activity with respect to CH 4 and NH~ oxidation. The addition of NH4C1 at 25 ~tg N g-1 soil strongly inhibited (78-89070) CH4 oxidation in the surface layer (0-15 cm) of a fine sandy loam and a sandy clay loam (native shortgrass prairie soils). The nitrification inhibitor nitrapyrin (5 gg g-~ soil) inhibited CH4 oxidation as effectively as did NH4C1 in the fine sandy loam (82-89%), but less effectively in the sandy clay loam (52-66%). Acetylene (5 ~tmol tool -1 in soil headspace) had a strong (76-100%) inhibitory effect on CH 4 consumption in both soils. The phosphoroamide (urease inhibitor) N-(n-butyl) thiophosphoric triamide (NBPT) showed strong inhibition of CH 4 consumption at 25 gg g-1 soil in the fine sandy loam (83%) in the sandy clay loam (60%), but NH~ oxidation inhibition was weak in both soils (13-17%). The discovery that the urease inhibitor NBPT inhibits CH 4 oxidation was unexpected, and the mechanism involved is unknown.