21 MPG combined is probably not the main reason someone buys a 2015 Porsche 911 Carrera 4S Cabriolet. This is a performance car, first and foremost, a machine engineered to deliver exhilarating speed, precise handling, and open-air thrills. Fuel efficiency is, at best, a minor concern for the individual who values the driving experience offered by a 3.8 liters flat-six engine and all-wheel drive.

City and highway performance

The EPA estimates the 911 Carrera 4S Cabriolet gets 19 MPG in the city and 26 MPG on the highway. These figures reflect driving a high-performance vehicle in different conditions. The city number considers stop-and-go traffic, frequent acceleration, and idling, all of which negatively impact fuel consumption. The highway estimate assumes more consistent speeds and less demand on the engine, resulting in better efficiency. The automatic transmission (AM-S7), Porsche’s PDK dual-clutch, surely helps highway numbers thanks to its ability to keep the engine in its most efficient RPM range while cruising. Ultimately, though, the driver’s style will significantly influence real-world results, making these figures useful for comparison but not definitive predictions.

Annual fuel cost

According to the EPA, the estimated annual fuel cost for the 2015 Porsche 911 Carrera 4S Cabriolet is $2,750. This figure is based on driving 15,000 miles per year, using fuel prices at the national average. This number gives potential buyers a general idea of the fuel expenses they can expect, but it’s important to remember that fuel costs fluctuate, and individual driving habits will play a major role. Someone who primarily uses the car for weekend fun will likely spend less, while someone who commutes daily in heavy traffic will likely spend more. Take a look at all Porsche fuel economy data to put this number in perspective.

Real-world expectations

Don’t be surprised if your real-world MPG numbers differ from the EPA estimates. Aggressive acceleration will punish your fuel economy, as will consistent use of Sport or Sport Plus modes, which hold gears longer for optimal performance. Gentle driving, maximizing coasting, and adhering to speed limits can help you achieve figures closer to the EPA estimates. The car’s trip computer provides real-time and average fuel consumption data, which can be used to monitor your driving habits and make adjustments. This remains a performance car, and focusing intently on extracting every last MPG likely defeats the purpose of owning a 911.

How it compares

Compared to its peers, the 2015 Porsche 911 Carrera 4S Cabriolet’s fuel economy lands where you might expect for its performance capabilities. For example, the 2015 Chevrolet Corvette Stingray Convertible (automatic) manages around 16 MPG city and 29 MPG highway, offering similar thrills with slightly better highway efficiency. A 2015 Jaguar F-Type R Convertible, with its supercharged V8, comes in around 16 MPG city and 23 MPG highway, showing the Porsche’s edge in everyday usability. The Audi R8 V8 Spyder from that year lags further, with a dismal 13 MPG city and 22 MPG highway. Customers who prioritize performance above all else rarely cross-shop based on MPG, but it’s helpful to see where the 911 falls in the landscape. Reviewing 911 MPG across all years can also add context.

Tips to maximize efficiency

While the 911 Carrera 4S Cabriolet is not predominantly about fuel efficiency, there are simple steps you can take to conserve fuel without sacrificing too much driving enjoyment. Use the standard driving mode for everyday commuting rather than Sport or Sport Plus. These modes are designed for maximum performance, and they burn more fuel accordingly.

Maintain proper tire inflation. Underinflated tires increase rolling resistance, which forces the engine to work harder, thus reducing fuel economy. Check your tire pressure regularly and inflate them to the recommended levels found on the sticker inside the driver’s side door jamb.

Anticipate traffic flow and avoid abrupt acceleration and braking. Smooth, consistent driving is more fuel-efficient than stop-and-go driving. Look ahead and try to maintain a steady speed whenever possible; after all, the glorious flat-six rewards drivers who let it sing in the higher registers.

Remove unnecessary weight from the vehicle. Extra weight increases the amount of energy required to accelerate and maintain speed. Leaving that extra set of golf clubs or heavy luggage at home can contribute to improved fuel efficiency, however marginal. And finally…

Limit the use of accessories such as air conditioning and heated seats. These put extra load on the engine and can reduce fuel economy, especially during short trips where the engine hasn’t fully warmed up. Rolling the windows down is a good compromise when the weather allows.