1. Use the best synthetic oil you can find. It will have superior lubricity characteristics, have a much higher TBN rating for protection from acids, greater protection against overheating, and lasts longer. Use good, low-micron primary filters, and good, extra-low-micron bypass filters. Your engines will never die OR wear out due to your oil. 2. If you change this oil at 500 hours (which would be way early), it's a once-a-year deal for almost everyone on this List. Anyone can drain oil once a year...and dispose of it properly. Re-read Jerry Munson's post about this..first class. 3. If you want to burn it in your engine(s), even 20 gallons of used oil can be burned by mixing it with 400 - 600 gal. of fuel (3.5-5% ratio). For the average trawler, that's about 130-180 hours of running, or the better part of a season. 4. We don't all run our boats at the same time, and there just aren't that many of us anyway. Spread our traveling out over a 6 month season, and the environmental concerns are pretty much a "wash". Really good comments from many of you on this. Love this List! Norm