Why only change the oil once a year? I suppose one might get by with a 12 month interval at the outside, but I would imagine most people hit the mileage interval well before that. I know some of the Hondas specify a 600 mile interval, some probably longer, but oil breaks down after it has been exposed to combustion by-products. I'd run cheaper oil before I stretched the change intervals that far. Certainly twice a year won't break the bank, and in severe climates, once a month has worked out very well for us (though I do cheat and follow the mileage spec on our Yam/Griz. At 800 miles per change, that means about 5-7 changes per year.)
