Once again if you are asking about a 2-stroke motor the following does not apply. If the motor was properly maintained you should expect the life expectancy of gas-power 4-stroke marine motor to be between 1000 and 1500 hours. Or, another way to think about it that every 100 hours is about 15,000 miles. Once again this is just a rule of thumb and many variables affect this range. If you are in the market for a used boat then I will also suggest you consider a marine surveyor: http://www.marinesurvey.org/ .