"Forget the hotel. I’m never leaving the Audi," I texted to one of the friends I was meeting for Jazz Fest in New Orleans when the spacious and luxurious 2014 Audi A8L TDI Quattro diesel luxury sedan arrived at my house.

The A8L diesel’s 36-mpg EPA highway rating and 860-mile theoretical cruising range put that boast to the test. I had to stop three times for breaks before the car needed refueling. It covered 740 miles at an average of 35.4 mpg and 67 mph.

The sumptuous but thrifty car made it from Detroit to just outside Tuscaloosa, Ala., on less than a tank of fuel. The diesel provided plenty of power for fast, smooth cruising.

The roomy and luxurious interior and Bang & Olufsen sound system kept me comfortable and entertained. The A8L’s built-in Wi-Fi hotspot allowed me to post my fuel economy online before I stopped for the night in Meridian, Miss.

The diesel, or TDI, version of the A8 is new for the 2014 model year. It just went on sale and is only available in the long-wheelbase version of Audi’s biggest and most luxurious sedan.

A8L TDI prices start at $82,500. The car comes with a 3.0-liter turbocharged V-6 diesel that produces 240 horsepower and 406 pound-feet of torque, an eight-speed transmission and all-wheel drive.

I tested a very well-equipped model with perforated leather seats; massaging, heated and ventilated front seats; adaptive cruise control; wood, aluminum and suede trim; Bluetooth connectivity; its own Verizon Internet account for Wi-Fi service; blind spot and lane-departure alerts; and 20-inch summer tires and 10-spoke wheels.

The A8L competes with the biggest and most luxurious all-wheel drive models of other top luxury sedans: the BMW 750Li xDrive; Jaguar XJL AWD, Lexus LS 460L AWD, Porsche Panamera 4S and Mercedes-Benz s350 Bluetec 4Matic, the only other diesel in the set.

The A8L TDI sneers at those cars’ fuel economy and blasts past as they stop to fill up at gas stations. This is very much the same tactic that allowed Audi to dominate recent runnings of the famous 24-hour race in Le Mans, France.

The diesels’ power might not match other automakers’ gasoline engines, but the Audis were virtually unbeatable because they went so much farther on a tank. Less time off the track refueling equals more time on the track, going fast and leaving the competition behind.

The A8L TDI’s EPA rating of 24 mpg in the city, 36 on the highway and 28 combined tops the competitors’ combined ratings by 3 to 9 mpg. In a competition automakers strive to win by 1 mpg, that amounts to lapping the field.

The A8L diesel also tops the EPA ratings of the hybrid BMW Activehybrid 7L, Lexus LS 600hL and Mercedes S400, even though none of them has all-wheel drive.

The engine’s horsepower trails most of the competitors, but the high-torque diesel and quick-shifting eight-speed transmission provide smooth and confident acceleration and plenty of power for long highway runs. The A8L TDI’s auto-stop function, which shuts the engine off at traffic lights and other brief halts, could stand to be smoother.

Audi’s MMI controller, which combines dials, multipurpose buttons and a video screen, allows you to adjust everything from the climate control and massaging seats to steering feel, throttle response and differential.

The system is the most user-friendly among German luxury brands. It’s less intuitive and requires more eyes-off-the-road time than some newer systems that rely on a touch screen, such as Cadillac’s CUE and Chrysler’s Uconnect.

The voice-recognition software is terrific. The controls for picking up and ending hands-free phone calls are inconveniently located, however.

The A8L’s interior look and feel are exceptional. Brown perforated leather seats, suede inserts on the doors and wood and aluminum trim lend a distinguished air. The A8L TDI’s room, comfort and features make it one of the few big luxury sedans that feel like a bargain; I’ve been in costlier cars that had less appealing interiors and fewer features. The trunk is a bit small, with less space than any of the competitors.

Despite my text, I was happy to exit the A8L when I reached New Orleans. But I was looking forward to the drive home, too. I’d had hours of bad weather and construction on the way south. With better conditions, could the Audi break 36 mpg in fast, real-world highway driving?

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2014 AUDI A8L TDI:

—Vehicle type: All-wheel drive five-passenger luxury sedan

—Engine: 3.0-liter direct-injected turbocharged DOHC variable timing 16-valve four-cylinder.

—Power: 240 horsepower at 3,550 rpm; 406 pound-feet of torque at 1,750 rpm

—Transmission: Eight-speed automatic

—EPA fuel economy rating: 24 mpg city/36 highway/28 combined. Diesel fuel.

—Wheelbase: 122.9 inches

—Length: 207.4 inches

—Width: 76.7 inches

—Height: 57.9 inches

—Curb weight: 4,586 pounds

—Base price (TDI): $82,500

—As tested: $98,550

—Rating: Four out of four stars

—Reasons to buy: Fuel economy, looks, comfort, features, all-wheel drive

—Shortcomings: Interior storage, operation of some controls, luggage room

All prices exclude destination charges.