I would run 15-40. Thats what I run in my Kubota's. In Oregon you could run an HDEO 10-30. I would not run a 20W. Rotella, Delvac, and Delo are quality oil at a good price. This tractor only holds four qts. so go with the good stuff and sleep well. FYI the hyd-trans holds 3.5 gallons.