A good-quality oil costs very little more than a poor-quality one. Yet it protects one of the largest investments you've ever made: your vehicle. A high-quality oil is especially crucial in these conditions. Do any of them apply to you?

Errand running. If you're stopping every few minutes, your engine never heats up sufficiently to evaporate the fuel contaminants in the oil. The unburned residues can contaminate your motor oil. You need an oil designed to take it.

City traffic. Poking along, idling at stop lights - it's just not good for your engine. It never warms up enough to evaporate the contaminants that circulate with the gasoline. But don't worry; a good-quality oil is cheap insurance.

Expressway driving. Actually, expressway driving is the optimum-most of the time. But if you drive long distances or near the maximum speed, your engine may become excessively hot, causing the oil to foam. Once again, a good-quality oil is the answer. The best oils contain additives that resist foaming.

An option-loaded car. Every time you choose an option: automatic transmission, air conditioning, power steering, and the like, you increase the operating temperature of your engine. That's hard on the oil-unless it's made with the best base stocks and a careful blend of additives.

A sub-compact car. We buy small cars for their economy. But we often push them to perform like their much larger relatives. Engines that work hard depend on the best oil for lubrication, cooling, cleaning, sealing, and easy start-up.

Infrequent driving. If your on-again, off-again driving habits resemble those of the legendary "little old lady," you're courting engine rust, corrosion and sludge. Moisture that forms in your engine during cool-down can rust metal surfaces and mix with your oil to form a thick gooey mess. And some of that moisture combines with leftover fuel residue to form acids that can corrode metal parts. Arm your engine with an oil that offers the film strength to maintain a complete coating on every part, so additives can conquer moisture and acids.

Towing. Towing heavy loads can heat your oil to as much as 300°F. You need an oil that can take that kind of heat-and keep you rolling.