The 9 Best Synthetic Oils

If you want one jug that suits most late-model gas engines, Mobil 1 Extended Performance is the safe choice. The label carries GM's dexos1 approval, and Mobil's data sheet lists the current API and ILSAC ratings. Mobil guarantees it for up to 25,000 miles between changes, but your owner's manual or oil-life monitor should still set the schedule. It also comes in thinner and thicker grades. You pay extra for a long-interval promise most drivers won't use.

Drivers whose manual names a GM, Ford or Chrysler oil code will find all three listed for Castrol EDGE. Castrol says it meets GM's dexos1 standard, two Ford specs and Chrysler's own, on top of the current API and ILSAC ratings. The black jug with the gold band is simple to pick out on a store shelf. Castrol's promise of 20,000 miles between changes is marketing, though, and the manual's interval still comes first.

The jug for Valvoline Advanced Full Synthetic already shows the newer GF-7A and SQ ratings, which helps if a dealer or shop asks for the current standard. GM's dexos1 mark is printed on the front as well. Valvoline claims much stronger wear protection than the industry test requires, but that comes from its own lab, not an outside one. It's sold in most grades, and the jug got a new look, so older photos may not match the shelf.

Made from natural gas instead of crude oil, Pennzoil Ultra Platinum starts from an unusually clean base stock. Its data sheet lists European ACEA ratings next to the U.S. API mark, and Pennzoil backs it with a 20,000-mile protection guarantee. This bottle is a single quart, handy for topping off or keeping in the trunk. Buying a whole oil change this way costs a lot more than buying a jug.

For drivers who change oil on the manual's schedule and want a full synthetic for less, Castrol GTX Full Synthetic makes sense. It carries the current API and ILSAC ratings, GM's dexos1 mark and two Ford specs, so it covers most domestic cars from recent years. GTX is Castrol's long-running everyday line, now made as a full synthetic. Castrol rates it for only 10,000 miles between changes, so it isn't meant for stretched intervals.

Once an engine passes about 75,000 miles, Mobil 1 High Mileage adds a seal conditioner meant to keep aging gaskets soft and slow small seeps. It still carries GM's dexos1 mark and the current ILSAC rating, and Mobil guarantees it for up to 15,000 miles. Think of it as upkeep for a tired engine rather than a repair. An engine that already drips oil onto the driveway will usually keep dripping.

Valvoline Restore & Protect is a cleaning oil: Valvoline says its additives lift piston deposits over several oil changes and stop new ones from forming. That suits a used car with a patchy service history or a small turbo engine that tends to build up gunk. The claim rests on Valvoline's own engine tests, and no outside lab has confirmed it yet. The payoff only shows if you stick with it for several changes in a row.

Plenty of German and other European cars call for a thicker oil and the carmaker's own approval code, and Mobil 1 European Car Formula is made for them. Mobil builds it for gasoline engines and for diesels without a particulate filter, which rules out most recent diesel cars. Before you pour, check that the code in your manual appears on the back label. It's also harder to find in small stores than everyday grades.

Idemitsu, a large Japanese refiner, made Idemitsu IFG3 for the thin oil that many Toyota, Honda, Subaru and Mazda engines call for. The jug carries the newer SQ and GF-7A ratings, and the formula is aimed at the knocking that small turbo engines can suffer when pulling hard at low speed. It's a fairly new listing with few owner reports so far, and the price is on the high side for a five-quart jug.