Isobutanol-extended fuel was tested in two recreational marine vessels placed in Annapolis, MD and operated for fifty hours on the Chesapeake Bay and surrounding tributaries. Field emissions testing was conducted using a unique portable marine bag sampling system (MPSS) which collected a weighted five mode composite emissions sample consisting of total hydrocarbons (THC), oxides of nitrogen (NOx) and carbon monoxide (CO) while operating recreational boats on both a non-oxygenated baseline indolene certification fuel and a 16.1% isobutanol-extended gasoline. Engine and boat runability was also observed throughout the six month operational period. In addition, back-to-back sampling yielded excellent repeatability from the portable bag sampling equipment. Based on the results of this preliminary study, isobutanol-extended fuels look to be very promising for marine engine applications. An introduction to biofuels policy in the U.S. and characteristics and highlights of butanol-extended fuels will be explored.