The probable limits of the carbon budget of the Rapid River Watershed, within the greater Glacial Lake Agassiz Peatland in northern Minnesota, were evaluated using a Monte Carlo simulation approach. Carbon enters the peatlands in groundwater, precipitation, and primary productivity. Carbon leaves the peatlands by groundwater and surface water outflow and by the outgassing of methane. Results of the simulations of the carbon budget show that the peatland is now probably a sink for carbon, supported by field data showing peat is, in fact, accumulating at the rate of about 1 mm yr-1 [Glaser et al., 1997]. Excluding extreme values, Monte Carlo simulation results indicate that the Rapid River Peatland stores between -28.98 g C m-2 yr-1 (release) and 50.38 g C m-2 yr-1 (storage) with a mean accumulation of 12.74 g C m-2 yr-1 over the 1,506,200 m2 watershed. The peatland appears to be delicately poised with respect to net gain or loss of carbon.