I usually run Yamalube 30w. It's what Yamaha reccomends and my bike has been running strong for 7 years and no rebuild yet. Recently the local sport shop ran out of the Yamalube and I was forced to try an alternative. The guy at the counter said that most of the pros use Honda oils. If you watch the tapes you can see the Suzuki and Kawasaki guys have Honda oils on the shelves. So, since I changed it last it's been Honda 10w40. That small change in oil weight isn't going to affect it much but I wouldn't run anything less than 30w. Definitely check out the back of the bottle when you buy oil though if you're not going to buy Yamaha oils. Make sure that the oil you buy does not have any friction modifier in it as that can ruin your clutch in a hurry.