Best Synthetic Motor Oil | Top Brands Compared

Industry specifications set pass/fail limits. When a brand says its oil delivers a certain percentage "more protection than required," it's comparing its own result to that limit, usually in testing it sponsored. That's useful information, but it isn't a head-to-head test against another brand. Published, independent comparisons that test all of these oils by the same method are rare.

How to weigh an oil claim

1. Independent laboratory testing with a published method carries the most weight.
2. Manufacturer-sponsored testing using standard ASTM or industry procedures is credible, but the manufacturer chose what to test and publish.
3. Published product specifications (approvals and typical properties) are factual, but describe minimums and typical values.
4. Marketing claims without a stated test method carry little weight.
5. Editorial recommendations, including the ones on this page, are opinions informed by the evidence above.

AMSOIL Signature Series

Signature Series is AMSOIL's extended-drain gasoline motor oil and the line with the widest grade range of the four. AMSOIL recommends it for up to 25,000 miles or one year in normal service and 15,000 miles or one year in severe service. AMSOIL's severe-service definition includes turbocharged and supercharged engines, short trips under ten miles, frequent towing or hauling, excessive idling and commercial use. That means many modern turbocharged vehicles fall under the 15,000-mile figure.

AMSOIL publishes several performance claims for the current formulation, all manufacturer-reported results against industry limits:

• 2X better protection against volatility than the API SQ limit in the Noack test (ASTM D5800), based on the 0W-20.
• 72% more protection against piston deposits than the Sequence IIIH test requires, based on the 5W-30.
• 4X more protection against LSPI than the standard requires in the Sequence IX test, using 5W-30 aged through a 25,000-mile service interval.

Check the specific grade's data bulletin for the specifications it lists before using it in a vehicle that requires an OEM approval.

Mobil 1 Extended Performance

Mobil 1 Extended Performance is the most widely available extended-drain synthetic in North America. Its product pages list API SQ, ILSAC GF-7A across 0W-20 through 10W-30, GF-7B for 0W-16, and GM dexos1 Gen 3 approval for the 5W-30. Mobil guarantees protection for 25,000 miles or one year, while also advising owners under vehicle warranty to follow the oil life monitor or owner's manual. Some of Mobil's own product text still references the earlier 20,000-mile figure, so read the current warranty terms.

Pennzoil Ultra Platinum

Pennzoil Ultra Platinum is built on PurePlus base oil, which Pennzoil makes from natural gas through a gas-to-liquids process. Pennzoil positions it around cleanliness and wear protection, and recommends following the vehicle manufacturer's drain interval. Its limited warranty adds 20,000-mile drain-interval protection, but only with conditions: exclusive use, a premium filter, topping off at least every 5,000 miles, enrollment, and an engine under 125,000 miles and 72 months old. For an owner who changes oil on the manufacturer's schedule, it's a well-documented premium choice.

Liqui Moly Leichtlauf High Tech

Leichtlauf High Tech 5W-40 is a European-specification oil. Its strength is its approval list: ACEA A3/B4, BMW Longlife-01, Mercedes-Benz 229.5, Porsche A40 and VW 502 00/505 00. Liqui Moly states it's for gasoline and diesel vehicles without particulate filters, so it isn't a fit for many newer European cars. It also doesn't carry ILSAC certification, which makes it the wrong choice for most domestic and Asian vehicles that call for ILSAC oils. Where its approvals match the manual, it's a strong option. Where they don't, it isn't. AMSOIL's European line covers the same ground in eight formulations, including low-SAPS versions for vehicles with particulate filters.

So which one is best?

The evidence doesn't support crowning a single winner for every engine. What it does support:

• AMSOIL Signature Series and Mobil 1 Extended Performance are the two published extended-drain flagships for gasoline engines, both at up to 25,000 miles or one year.
• AMSOIL publishes the most extensive set of test claims, but nearly all of them are manufacturer-reported.
• Pennzoil Ultra Platinum and Liqui Moly are premium oils built around manufacturer intervals and approvals rather than extended drains.

Editorial recommendation: Vyscocity recommends AMSOIL, matched to how the vehicle is maintained. Signature Series for the longest documented drains, Extended-Life for drains up to 20,000 miles, OE for the manufacturer's schedule and the AMSOIL European line for vehicles that require European approvals. Matching the line to the interval means you never pay for drain capability you won't use.

Price per quart is the wrong number to compare. What matters is cost per mile:

Cost per mile = (oil + filter + labour) ÷ miles between changes

The example below uses round illustrative figures, not current prices. Plug in your own numbers.

The pattern holds whatever the actual prices are. A premium extended-drain synthetic only costs less when you run the interval it's built for. Change it early and you pay more for the same mileage. Add oil analysis to the extended scenarios if you want the interval verified, and the math still usually favours the longer drain when you factor in fewer shop visits. That's exactly why AMSOIL builds OE for manufacturer intervals and Signature Series for maximum drains. Buy the line that matches the interval you'll run.

For AMSOIL buyers, the AMSOIL Preferred Customer program lowers product cost; AMSOIL advertises savings of up to 25% on orders. Details are on the AMSOIL Preferred Customer page. Orders ship from AMSOIL's own distribution centers.