I worked in the petroleum industry from 1993 to 2000 in various refining and marketing capacity including a 2 year stint at a major refinery in Southern California as a crude oil planner/buyer. This job also entailed setting the gasoline blending formula from time to time.

I know many of you are Rover enthusiasts and auto enthusiasts. My first advice is stop filling your vehicles with "Premium Only" gasoline as "required by the manufacturer". Your vehicle's fuel management system working in conjunction w/ the oxygen sensor will adapt to the octane level of the gasoline you use. You might notice a very slight loss of power at the very limits of your engine if you were redlining with each shift, or if your vehicle is heavily laden and you are climbing a mountain. For 95% of normal day to day driving conditions, 87 octane gasoline will do just fine. If you happen to live in a high altitude area and lower octane gasoline is available, feel free to go even lower.

My last 3 vehicles (00 Disco Series II, 93 BMW 740i (e32) & Volvo 850 Turbo Wagon - all were required "Premium Gasoline Only" ) were on strict diet of 87 octane gasoline for combined 200,000+ miles. If I knew I were heading on a road trip w/ full load, I would use 89 octane to handle occassional hill climbing/passing situation.

And about the mid grade/89 octane gasoline - this is simply 50/50 blend of 87 octane and 91 octane gasoline. Refineries do not blend 89 octane - only 87 octane and 91 octane gasoline. When you pump 89 octane gasoline at your local station, it is being mixed at the pump at 1 to 1 ratio. That's why the price difference between the 3 grades are almost always consistent (typically 10 cents per gallon between grades).

If you were a penny pinching driver (hey, I resemble that remark) and notice that 87 octane is priced much lower than 91 and 89 octane, you can blend your own mix at the pump by buying half tank of 87 octane and half tank of 91 octane for a discounted 89 octane tank.

On another note, there is very little difference between different brands of gasoline. All refineries and storage tank farms use common gasoline pipeline to transport the fuel. Many times, a batch of fuel (in Southern California, minimum 5,000 barrels or 210,000 gallons) may get traded from one company to another depending on their supply situation. Every gallon of gasoline is virtually the same stuff. The only difference between a Shell gasoline and ARCO gasoline is the fuel additive added at the distribution terminal as the trucks are loaded with fuel. There is very little difference among the additives. If you want to feel more sure, use fuel system cleaners once a year - this is typically done at major service intervals by the dealer/repair shop. Don't buy the marketing hype of various petroleum companies. In fact, Costco gasoline in Southern California is supplied by Shell refinery without Shell's own fuel additive.

Happy motoring!