Naming standards were in flux at Oldsmobile during the late 1930s and 1940s. From 1932 through 1938 Oldsmobile had two series: "F" and "L". F-Series came with a straight 6 engine and L-Series came with a larger body and a straight 8 engine. The F-Series was replaced by the Series 60 in 1939 and L-Series was replaced with the Series 70. The Series 60 used the GM A-body and the Series 70 used the B-body. In 1940 the even larger C-body was introduced to Oldsmobile and it alone was powered by the straight-8. The series were also given names for the first time that year with the Series 60, 70, and 90 being called the Special, Dynamic, and Custom Cruiser respectively. In 1941 both engines were offered on each series so to differentiate between the two the second digit was used to denote the number of cylinders, so the Custom Cruiser 90 was replaced with the Custom Cruiser 96 and 98. In 1942 Oldsmobile dropped the six cylinder Series 90 model leaving only the Custom Cruiser 98.
The new C-body that the 1940 Oldsmobile Custom Cruiser Series 90 shared with Cadillac Series 62, Buick Roadmaster and Super, and the Pontiac Torpedo featured cutting-edge "torpedo" styling. Shoulder and hip room was over wider, running boards were eliminated, and the exterior was streamlined and lower. When combined with a column mounted shift lever the cars offered true six passenger comfort. The 90 rode on a wheelbase of . A total of 43,658 90s were sold in four body styles. The rarest was the 4-door convertible with only 50 being sold.
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In 1942 the Custom Cruiser 98 was once again the Oldsmobile entrant into the luxury market. Gone was the single year offering of the 96. All cars in this series were powered by the straight eight engine. Also gone in this shortened model year was the ultra rare 4-door convertible. An exclusive inch wheelbase was used in the series. A total of 6,659 98s were made before production was shut down due to World War II. To celebrate the company's 44th anniversary all Oldsmobiles received a small badge on the grille with "B44" attached. This was not a model designation.
| length = 1948–49: <br />1950: <br />1951: <br />1952: <br />1953: Total sales set yet another record of 106,220.
1951
thumb|left|1951 Oldsmobile 98 Deluxe Holiday Sedan (with non-standard wheels)
The 98 topped the Oldsmobile line again for 1951 with Three body styles available. The 4-door sedan and convertible came only with Deluxe equipment, while the Holiday hardtop was available with either Deluxe or Standard trim. The 98 standard equipment included bumper guards, cigarette lighter, dome light, rubber floor mats, stainless steel moldings, lined trunk, illuminated ashtray, foam rubber seat cushions and extra chrome moldings. Deluxe equipment was special rear door ornament, rear center armrests, Deluxe electric clock, Deluxe steering wheel with horn ring and special chrome trim. Upholstery choices were nylon cord, nylon cloth and leather. The pillared Club coupe was no longer offered. With the only choice in a closed 2-door 98 now being the hardtop, Holiday sales nearly doubled to 17,929 units.
1952
thumb|left|1952 Oldsmobile Ninety-Eight Holiday Coupé
From 1952 the car, which remained as the top of the line Oldsmobile, began to be called Ninety-Eight. This would continue until the demise of the model, with the exception of model years 1957 and 1961. The series shared the higher output 160 HP Rocket V8 with the Super 88s. Standard equipment on the three body styles included bumper guards, gray rubber floor mats front and rear, electric clock, dual horns, aluminum door sill plates, chrome gravel guards, foam rubber seat cushions, turn signals, carpeting front and rear, stainless steel wheel trim rings, windshield washer, and Deluxe steering wheel with horn ring. Upholstery selection was broadcloth or six colors of leather. Standard tire size was by . For the first time power steering was an option. Another new option was the Autronic Eye, an automatic headlight dimmer, which in its initial year was shared only with Cadillac.
1953
thumb|left|1953 Ninety-Eight Fiesta
thumb|98 Fiesta style "spinner" hubcap
New in 1953, the Fiesta joined the Cadillac Series 62 Eldorado and Buick Roadmaster Skylark as top-of-the-line, limited-production specialty convertibles introduced that year by General Motors to promote its design leadership. It featured a cut-down belt line, a wraparound windshield that was lower than the standard Ninety-Eight's windshield, and special "spinner" hubcaps, which became a trademark on later Oldsmobiles. Virtually every Oldsmobile option was standard except air conditioning, regarded as unnecessary at the time in a convertible.
Mechanically, the Fiesta had a special version of the Ninety-Eight engine which gained 5 horsepower to 170 through manifold streamlining and compression increased from 8.1:1 to 8.3:1. A four-speed Hydramatic automatic transmission and faster rear axle ratio were designed to keep the 4,459 pound shipping weight Fiesta (336 more than a standard Ninety-Eight convertible) up to Oldsmobile performance standards. At US$5,715 ($ in dollars ) (over $700 ($ in dollars ) more than the Skylark) the Fiesta was nearly twice the US$2963 price ($ in dollars ) of a standard Ninety-Eight convertible, with only 458 units produced to its 7,521.
Standard equipment for 1953 included bumper guards, electric clock, lined trunk, dual horns, cigarette lighter, chrome moldings, twin interior sun visors, rear seat robe rails, special rear stainless steel trim, chrome window ventiplanes, windshield washer, and Deluxe steering wheel with horn ring. In 1953 a padded safety dash also became standard on the Ninety-Eight. For the first time air conditioning was an option.
The Fiesta convertible would be gone the next year but its name would be resurrected in 1957 for Oldsmobile station wagons.