I had been running Pennzoil 5W-30 in my Mazda 626, did an Auto-Rx treatment and switched to Redline 10W-30 on March 3. My mileage immediately increased 7.1% from 21.2mpg to 22.7. Also the car seems to have a bit more pep. During this time I used the same gas (Mobil regular), checked the air pressure in the tires, and did the same type of city driving. (If anything I drove more aggressively with the Redline in.) Now after a few tanks of gas I am sure the mileage increase is not a fluke. The only thing I can think of other than the oil is a possible reformulation of the gasoline to summer blend. But,it seems early in the year for this to happen. If Redline really does increase mileage it makes it a very economical oil to use. Has anyone else noticed a MPG increase? Can you think of any other reason besides the oil that would cause this change?