A. This question is perhaps the most hotly contested out of any questions ever asked about the Virago. Some say that the "wet clutch" in a motorcycle requires special oil to withstand the greater "sheer forces" on the oil causing it to break down faster. Others will tell you they use and have used the local gas station's cheaper oils since they got their bikes. To solve the issue of the personal feelings about the real facts behind the use of oil, I offer this study on the differences between "Motorcycle Oils" vs. "Automotive Oils"
Comments: After reading that the study cited found that Castrol GTX motoroil came in second only to the more expensive synthetic based oils, and performed better on average than the grossly more expensive "Motorcycle Oil" tested, I prefer to use only Castrol GTX 20w 40 in the Summer, and Castrol GTX 10w 30 in the cooler Spring and Fall months.

Additional Information: Yamaha recommends the following:
Engine oil
    40 F and above        SAE20W/40, SE-SF
    40 F and below         SAE10W/30, SE-SF