The 1957-61 British XK-150 was the last of Jaguar's famous "XK" sports cars, and the one best suited to America.

The XK-150 was preceded by the gorgeous Jaguar XK-120, which was a sensation in the early 1950s. But Americans soon wanted more refinement. Jaguar thus gave them the mid-1950s Jaguar XK-140, which had the XK-120's lithe styling but featured more comfort and power.

The XK-150 was the most mechanically developed of the XK line, and also was the plushest, most-civilized version. Although sleek, it was the least sexy looking XK model because it was a bulkier version of its predecessors, with a wider body, higher front fenders, recountered belt line below the windows and a larger grille.

The XK-150 was less of a pure sports car than its predecessors, but the U.S. market was demanding more sporty "touring" cars than outright sport cars, which were generally uncomfortable for anything but short trips. Still, the XK-150 had impressive performance and handling.

The XK-150's one-piece curved windshield replaced the old XK two-piece "windscreen," and the car had more power. Some Jaguar fans disliked how the XK-150 looked, but it appealed to a wider audience in America -- a huge Jaguar market.

The XK-150 had more interior room and the new grille allowed better engine cooling. Bumper appearance and protection were improved, and old-fashioned interior walnut gave way to leather. Nearly all XK-150s had sporty wire wheels.

The XK-150 retained the basic heavy, massive chassis, stiff manual transmission and race-winning 3.4-liter inline six-cylinder engine of the XK-140. But the new model was updated with four-wheel disc brakes, when even Cadillacs and Corvettes didn't have them. The "discs" replaced the XK's old fade-prone drum brakes. Jaguar knew disc brakes would be very effective because they were on its successful C- and D-Type sports/racing cars.

The XK-150 initially was sold only as a coupe and convertible but soon also came as a sportier roadster, which Jaguar called an "Open Two Seater" (OTS). The roadster lacked the rakish, lowered door sides of earlier XK roadsters, but it was the first XK roadster with roll-down windows instead of detachable plastic side curtains. It also was the first XK roadster with exterior door handles.

The XK-150's engine's standard horsepower was 190, but the XK-150's added weight -- 3,220 to 3,520 -- led many to order it with the optional 210-horsepower version of the six-cylinder, which also produced more torque. Many also ordered the car's four-speed manual transmission with optional overdrive for more relaxed highway cruising. It was a sign of the changing sports car market that an increasing number of buyers ordered the optional three-speed automatic transmission. The few other options included a radio.

Jaguars were attractively priced, but never inexpensive. They attracted many older affluent buyers who didn't want to shift gears with the car's manual transmission. Women who liked the XK-150's still-sleek lines also welcomed an automatic. The XK-150 was too heavy to be raced, but a fair number with automatics were seen in parking lots in affluent areas, driven by women.

The manual transmission XK-150 was the fastest Jaguar because a 250-horsepower "S" version of its engine arrived for all models in early 1958 with a revised cylinder head, three big carburetors, lightened flywheel, higher compression and wilder camshaft timing. Then Jaguar enlarged the engine from 3.4 to 3.8 liters for 1959 and offered another "S" version with a whopping 265 horsepower.

The 265-horsepower XK-150 S, which came only with a manual gearbox, did 0-60 mph in 7.4 seconds and reached 136 mph. That was very fast for the late 1950s -- and even quick by today's standards. Like all Jaguar engines, the "S" was smooth and docile. Fuel economy of any XK-150 was good for a fast, heavy sports car, at 20 mpg on highways because it was fairly aerodynamic.

Sales of the XK 150 S with the 3.8-liter six-cylinder totaled 1,466 models, which makes them the rarest of the XK-150s.

The XK-150 was built from May 1957 to October 1961 and it sold for about $4,500-$5,200. It's now valued at $66,600 for a coupe in top condition to $152,000 for a roadster with the "S" engine -- although one price guide puts an XK-150 S roadster at $175,000. One sold at an over-the-top price of $269,500 at Gooding's Pebble Beach auction in 2006. Whatever -- XK-150 prices keep rising.

The XK-150 with any version of the 3.4- or 3.8-liter six-cylinder sold well for a sports car from a fairly small automaker. Sales totaled 9,395 cars, up from 8,884 for the XK-140. (Sales of the longer-lived XK-120 -- introduced overseas in 1948 -- were 12,087 cars.) About 7,000 XK-150s were sent to America.

The basic XK line had become pretty old when replaced in 1961 by the sensational 150-mph Jaguar E-Type sports car. It was influenced by Jaguar's D-Type sports/racing car, and Jaguar insiders called it "the miracle car." But Jaguar's "XK" sports cars had become so famous in America that the 1961-75 E-Type commonly was referred to here as the "XK-E."