Microbial consumption is the dominant sink of oceanic carbon monoxide (CO), one of the major carbon-containing photoproducts of chromophoric dissolved organic matter in marine waters. This study presents first-order microbial CO consumption rate constants (kCO) determined using whole-water dark incubations in summer and fall in diverse marine ecosystems covering the Delaware Bay, NW Atlantic, and Beaufort Sea. The microbial CO consumption rate constant, kCO (mean ± SD) was 1.11 ± 0.76 h–1 in the Delaware Bay, 0.33 ± 0.26 h–1 in the coastal Atlantic, 0.099 ± 0.054 h–1 in the open Atlantic, 0.040 ± 0.012 h–1 in the coastal Beaufort Sea and 0.020 ± 0.0060 h–1 in the offshore Beaufort Sea. The kCO in the Delaware Bay covaried with chlorophyll a concentration ([chl a]), rising with increasing salinity in the range 0 to 19 and diminishing with further increasing salinity. The kCO in the Beaufort Sea is significantly positively correlated with [chl a]. Both the Atlantic and cross-system data sets showed significant positive correlations between kCO and the product of [chl a] and water temperature, suggesting that [chl a] can be used as an indicator of CO-consuming bacterial activity in the areas and seasons sampled in this study. Microbial CO consumption was shown to follow Wright-Hobbie kinetics, with variable but low half-saturation concentrations: ~1 nM in the Beaufort Sea and Gulf Stream and 2 to 18 nM in the coastal NW Atlantic. These low half-saturation concentrations suggest that microbial CO consumption in seawater is at times partly saturated, and that some previous microbial CO consumption rates determined with the commonly used 14CO method could be underestimates due to the addition of 14CO as a tracer substrate. The present study provides valuable data for coastal and Arctic waters whose kCO values are poorly or not constrained, including extensive data on the dependence of kCO on the concentration of CO.