Do I believe Volvo only uses parts of the highest possible quality, regardless of cost?? Not really!! Actually, I believe that Volvo, like every other manufacturer, compromises between cost and quality. I suspect they use the cheapest parts available that meet their minimum standards of performance and reliability. OEM spark plugs are probably fine, but it's a stretch to say they're the best available. Ditto with tires, brakes, audio components, upholstery, lights, and most everything else on the car.