Best Overall
Mobil 1 Extended Performance

A long-lasting lubricant with exceptional cleaning additives.

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Budget Oil
Castrol GTX Magnatec

A budget-friendly motor oil that offers above-average engine protection.

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Best For
Diesel Engines
Shell Rotella T6

A solid synthetic option for diesel drivers that want greater protection on the road.

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Green Option
Pennzoil Ultra Platinum

A high-performance oil that combines longevity and green technology.

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Best For Old Cars
Valvoline High Mileage

A great blend for older vehicles that has detergents to prevent sludge.

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Getting an oil change can feel mundane, but swapping out the goop in your engine ensures performance down the line. Although you can use conventional oil, the best synthetic oils can bolster your engine and keep it running smoothly. But how can you tell which one is the right choice for your car?

This in-depth review will look at some of the best synthetic motor oils on the market based on the benefits they offer your engine. We’ll also talk about the difference between a full synthetic and a synthetic blend and go over a couple of industry terms to help you pick the best oil for your engine.

#1 Best Overall: Mobil 1 Extended Performance Full Synthetic Motor Oil

From the brand that carries the NASCAR seal of approval, Mobil 1 Extended Performance is a full synthetic designed for the long haul. It’s No. 1 on our list of best synthetic oils thanks to Mobil 1’s claims that this formula protects critical engine parts for one year or up to 20,000.0 miles, whichever occurs first. Having additives that keep oil from breaking down and provide strong sludge and deposit protection also helped it earn the top spot.

The oil holds current American Petroleum Institute (API) and International Lubricant Specification Advisory Committee (ILSAC) GF-6A licenses (which we explain near the bottom of this article) and is compatible with multiple Ford and General Motors lubricants. It also works in cars ranging from daily drivers and high-performance cars to trucks and vehicles with diesel engines.

Key Features

  • Cost: $.20/fluid ounce (fl. oz.)
  • Follows ILSAC GF-6A standards for low-speed pre-ignition
  • Designed to prevent and clean sludge buildup in car engines
  • Has an oxidation-controlling additive to prevent oil breakdown
  • Rated for protection up to 20,000.0 miles

What Customers Are Saying

Amazon Review Score: 4.8 out of 5 based on over 32,000 ratings

Customers like the durability and price point of the product, but a few reviews mention the oil burning quickly. Overall reviews are positive with customers saying engine performance remained smooth.

#2 Best Budget Oil: Castrol GTX Magnatec Full Synthetic Motor Oil

Drivers looking for full synthetic oil that offers performance at an affordable price should check out the Castrol GTX Magnatec series, which we awarded the title of Best Budget Oil. Castrol says it offers six times better protection than industry standards, citing the Sequence IVA Test that measures common engine wear.

In terms of compatibility, the GTX formula works with the second generation of General Motors  Dexos 1® oil at viscosity grades 0W-20, 5W-20, and 5W-30. Along with the budget-friendly price point, this full synthetic oil clings to critical engine parts throughout the entirety of the drive cycle, helping reduce the amount of wear that happens during idling and stop-and-go driving.

Key Features

  • Cost: $.31/fl. oz.
  • Additive molecules that stick to the engine throughout the drive cycle
  • Above-average sludge protection, per API
  • -49 degrees Celsius pour point
  • Works well in temperate climates

What Customers Are Saying

Amazon Review Score: 4.8 out of 5 based on over 17,000 ratings

In terms of ratings, Castrol GTX Magnatec is one of the best synthetic oils on Amazon with its high review scores. The overall value and quality appeal to buyers, but some mention the oil being thicker than anticipated at lower temperatures.

#3 Best For Diesel Engines: Shell Rotella T6 Full Synthetic Diesel Engine Oil

Diesel owners looking for synthetic engine oil may find the Shell Rotella T6 formula a winner. This offering from the Netherlands-based company promises a 1.5-percent increase in fuel economy compared to 15W-40 oils but recommends that motorists follow their manufacturer’s guidelines for best results.

Additives in the Rotella cocktail help protect against soot, dirt, and other debris, and the oil has improved wear protection from the previous generation of diesel engine lubricants. It also shows an improvement in engine protection compared to the older API CJ-4 oils.

Key Features

  • Cost: $.19/fl. oz.
  • Improved fuel economy
  • Low-ash formulation for cleaner emissions
  • Improved heat resistance to prevent oil breakdowns
  • Resists viscosity loss

What Customers Are Saying

Amazon Review Score: 4.8 out of 5 based on 10,000 ratings

Diesel owners seem to dig the Rotella formula, as customers mention how well the oil worked across brands like Subaru and motorcycles, and many call it a great value. On the other hand, finding debris in the oil and leaky bottles is brought up in negative reviews.

#4 Green Option: Pennzoil Ultra Platinum Full Synthetic Motor Oil

If you demand the best of your car, then Pennzoil Ultra Platinum has probably caught your eye. Within the golden-colored case is a motor oil not derived from crude oil, but rather natural gas. Besides being carbon-neutral, Pennzoil claims its products protect horsepower and boost fuel economy, which is why it earns a spot on our list of the best synthetic oils.

As the factory choice for all of Dodge’s Street and Racing Technology (SRT) high-performance vehicles, this oil is meant to live in the fast lane. It’s a solid choice whether you’re hitting the racing strip or towing a heavy load.

Key Features

  • Cost: $.27/fl. oz.
  • Adds an average of 550 miles per year in fuel economy
  • Cleans pistons better than the industry standard
  • Carbon-neutral product
  • Maximizes high-performance engines

What Customers Are Saying

Amazon Review Score: 4.8 out of 5 based on 10,000 ratings

Buyers praise the longevity and performance of this formula, but complaints include bottle leaks and the high price. One customer specifically mentioned a stronger cold start and better performance in the high-rev range.

#5 Best For Old Cars: Valvoline High Mileage Synthetic Blend Motor Oil

Valvoline High Mileage is a synthetic blend made for vehicles that have logged over 75,000.0 miles. The MaxLife Technology® works to protect against friction, wear, heat, and deposits in the engine. It also uses conditioners that work to strengthen seals in order to prevent leaks and lessen existing ones.

Valvoline recommends that motorists, especially those who are stop-and-go drivers, swap out their oil roughly every 3,000.0 to 4,000.0 miles. Since synthetic blends still contain petroleum oil, you usually have to change the oil more frequently compared to full synthetic options.

Key Features

  • Cost: $.25/fl. oz.
  • Added antioxidants help resist motor oil breakdown
  • Includes detergents to prevent sludge
  • Includes seal conditioners to delay oil leaks
  • Geared toward high-mileage engines

What Customers Are Saying

Amazon Review Score: 4.8 out of 5 based on 14,000 ratings

The affordable price and easy-pour design are additions customers like. Multiple reviews mention great performance in their high-mileage vehicles. The most common gripe from buyers is a leaky bottle.

Why Cars Need Motor Oil

Motor oil is a crucial part of an engine’s performance. At a base level, motor oil lubricates moving parts within the engine and helps prevent unwanted metal-on-metal contact. Less contact means less wear and thus fewer repairs you’ll have to pay for.

From Conventional To Synthetic 

Motor oil has evolved from gunky fossil fuels to a complicated formula that does more than just keep an engine running smoothly. Conventional motor oil is made from petroleum, and its natural composition is prone to creating sludge in engines. There are conventional petroleum oils that use additive packs to help prevent sludge, but using the old formula means changing your oil more often.

Synthetic oil is different by design. Based on modified petroleum components, the best synthetic oils are manufactured to contain fewer impurities and therefore less sludge than conventional oil. Oil brands also use additive technology so their products can better preserve engine life.

Common additives include:

  • Anti-wear additives
  • Cleaning agents to fight corrosion
  • Antioxidants to help with oil breakdown in extreme temperatures

Best Synthetic Oils Buyers Guide

With so many brands offering unique and innovative versions of motor oil, choosing the best synthetic oil for your car depends on a mix of factory specifications, what performance you expect out of your vehicle, and your personal budget. It is also important to have an in-depth understanding of synthetic oil in comparison to different engine oils so you can get the best product for your vehicle.

Full Synthetic Vs. Synthetic Blend

Even though oil has come a long way, you still get what you pay for. Full synthetic is a lab-created oil base with additives that protect the engine. A synthetic blend oil contains a mix of conventional motor oil and man-made lubricant.

While a synthetic blend offers better engine protection than the old stuff, it still has impurities that can lead to sludge. It’ll handle exceptionally high and low temperatures better than conventional oil, but the upgrade to full synthetic oil isn’t usually that much more expensive than a synthetic blend.

Oil Change Intervals

You’ve probably heard plenty of times to change your oil roughly every 3,000 miles, and that’s a pretty decent guideline if your car uses conventional crude oil. However, cars compatible with full synthetic oil can go much longer without swapping out lubricant, especially if you use one of the best synthetic oils.

Brands like Royal Purple sell oil products that last well into the 10,000-mile range, and Mobil 1’s Extended Performance claims to offer wear protection for up to 20,000 miles. That said, your style of driving and usual mileage will depend on when you need to change your oil. You should also make sure to change oil filters routinely to ensure the engine can perform in peak driving conditions. When in doubt, always follow your manufacturer’s recommended service intervals.

Oil Viscosity

One of the biggest tests for motor oil is the thickness at varying temperatures. The higher the viscosity, the higher the density. Modern oils are manufactured to work properly in fairly extreme temperatures, but you should pay attention to the pour point outlined by the manufacturer. That will tell you which cold and high temperatures you can pour the oil out of the container, which is good to know if you live somewhere that experiences severe cold weather.

Car manufacturers will specify in the owner’s manual what viscosity is compatible with their vehicles, so just make sure to match the label if you’re doing an oil change at home.

API Terms

The American Petroleum Institute issues categories for oil performance and denotes how oil manufacturers can brand products. Here’s an overview of common terms you’ll see that relate to the API’s standards:

  • International Lubricant Specification Advisory Committee: ILSAC uses API standards for oil licensing for quality. Current ILSAC classifications include GF-6A and GF-6B, so you’ll want to make sure whatever you buy is compliant with those terms.
  • Resource conserving: This label is intended for oils in cars, vans, and light trucks that may result in greater fuel efficiency.
  • Performance level: Oils can have various performance levels, and the API updates these as manufacturers advanced engine technology.  Current engine terms include:
CategoryVehicle Compatibility
SP2020 and older automotive engines
SN2020 and older automotive engines
SM2010 and older automotive engines
SL2004 and older automotive engines
SJ2001 and older automotive engines

The API also says newer performance levels work retroactively, so an oil-rated SP will work if a manufacturer calls for an SM. It also provides ratings for diesel engines:

CategoryVehicle Compatibility
CK-42017 and newer diesel engines
CJ-4Diesel engines from 2010-2016
CI-4Diesel engines from 2002-2009
CH-4Diesel engines from 1998-2001

Unlike gasoline-powered vehicles, diesel categories are not backward compatible.

Our Review Standards

When choosing the best synthetic oils profiled in this review, we picked some of Amazon’s top-selling products and looked at overall engine protection, strong customer reviews, and competitive prices.

Why You Can Trust Us

Each year, we review over 1,000 auto products. Our team of product experts thoroughly researches top products and tests items on real vehicles when possible before making our recommendations.

We publish hundreds of product and service reviews to bring car enthusiasts detailed guides on automotive tools, detailing kits, car seats, pet products, and much more. For more information on our testing methodology and how we evaluate every product, check out our methodology page here.

*Data accurate at time of publication.