Methanotrophs were up to 1 and 0.65% of the total counts in estuarine waters and offshore sediments respectively. Experimental tests on methanol utilization showed that the estuarine isolates grew best at 4% methanol whereas offshore ones grew at 5% at an optimum pH of 6 or 7. Methanol, when used as an additional carbon source, in the presence of nutrient broth concentration ranging from 0.08 to 0.4%, enhanced growth by 129% and respiration by 177% in estuarine isolates. Biochemical and physiological characteristics showed that estuarine methylotrophs exhibited taxonomic affinities to Pseudomonas I or II sp. The offshore genera were more varied and belonged to Flavobacterium and Pseudomonas I or II sp. The abundance, activity and identity suggest that these physiological groups could be widespread and therefore could perhaps contribute significantly to the changes in C1 compounds and even their derivatives in marine and estuarine environments.