In Maine road diesel is pale yellow in color and marine diesel is died red. Other than that I think that road diesel has a lower sulfur content. Consequently, it might be desireable to add a lubricity enhancer if you are running road diesel in an older engine. With a new engine you are probebly OK with road diesel. However in 2012 all diesel is limited to 15ppm sulfur maximum. Thus in 2012 the only difference will be the color and the taxes included in the price.