3 per year, one in Dec., one in March, and one in summer when I go for vacation. I keep a watch on GM oil life monitor, they usually dont go below 50%, 3% oil life drop per 1000 miles, I use synthetic, I am convinced I do not need synthetic, but buy synthetic any way, (habit, can not stop)
2003 Pontiac Montana,3 pear year,
2001 Chev Malibu that I take care of, only 2 changes per year.
Middle TN, and tough summer vacation service.