Q. What is the difference between Aspen 2 and Aspen 4? A. Aspen 2 contains 2% fully synthetic oil and is suitable for machines such as chainsaws, strimmers, hedgetrimmers and other air cooled 2-stroke engines. Aspen 4 is alkylate petrol without any added oil and is suitable for machines such as lawnmowers, stump grinders and other 4-stroke powered machines. It is also a great alternative fuel for camping stoves and lanterns.