I have a 2006 Nissan Frontier 4WD V6 Automatic King Cab Truck. The owner's manual has the following to say about fuel:
For 4.0L engine. Use unleaded regular gasoline with an octane rating of at least 87 AKI (Anti-Knock Index) number (Research octane number 91). For improved vehicle performance, NISSAN recommends the use of unleaded premium gasoline with an octane rating of at least 91 AKI number (Research octane number 96).
For the first year and 30K miles I used nothing but regular. I keep detailed gas purchase records and has as been my experience in the past, the fuel economy gradually increased as the engine was broken in. After the fuel economy stabilized, I decided to do a comparison test between regular and premium fuel. I alternated regular and premium fuel for extended periods (5251 miles of regular, 2174 of premium, 5150 of regular, 2916 of premium,
926 of regular). I did not include the transition tanks of gas in the miles or gas usage. Total mileage on regular was 11,327. Total mileage on premium was 5,090. Average fuel economy on regular was 19.4. Average fuel economy on premium was 19.8. I never detected any difference in performance. I'd say that it is certain that the use of premium resulted in a detectable increase in fuel economy - something in the 1% to 3% range. Since premium fuel cost 5% to 8% more than regular, it seems that the use of premium is not justifiable on economic grounds. Plus fuel cost only 2% to 4% more, so I may experiment with plus fuel to see if it yields similar fuel mileage increases.Ed