The C18 was unveiled at the Museum Tinguely in Basel, Switzerland. It was conceived as a clear evolution of the C17, with the most significant technical upgrade being the Ferrari-derived SPE 03A engine — again badged as Petronas — paired with a seven-speed gearbox, the first time Sauber had used a seven-speed unit. The car also switched to Bridgestone tyres, a first for the team, after Goodyear withdrew from Formula One before the 1999 season.
Pedro Diniz's arrival brought an estimated seven million dollars in personal sponsorship funding, and with savings from not retaining Johnny Herbert's salary, the team was estimated to have approximately twelve million additional dollars available for the C18's development. Diniz also brought Parmalat sponsorship, though this triggered a legal dispute with his former employer Arrows that was not resolved until 2002.
In early testing, the C18 suffered some mechanical teething issues, but both drivers reported satisfaction with the car's feel. By mid-February, Alesi was classified fastest during a Barcelona test, ahead of McLaren and Jordan. Shortly after the season-opening race, Technical Director Leo Ress confirmed that the C18 had featured a flexible rear wing, before the FIA introduced a standardised flexibility regulation ahead of the Brazilian Grand Prix.
The C18 retained the two-tone blue livery of its predecessor, with Red Bull and Petronas among the prominent sponsors. A Malaysian flag appeared on the engine cover at the inaugural Malaysian Grand Prix to mark the occasion.
The 1999 season was a difficult one for the team. Mechanical failures and reliability problems meant that a C18 crossed the finish line in a Grand Prix on only 12 occasions across the whole campaign. Diniz retired from 12 of his 16 races and did not finish a Grand Prix until the Canadian round, the sixth of the year. Alesi fared somewhat better with eight retirements, and scored the team's first points of the season with a sixth-place finish at the San Marino Grand Prix. Diniz subsequently contributed sixth-place finishes at the Canadian, British, and Austrian Grands Prix. Alesi added the team's final point with a sixth at the Japanese Grand Prix — the season's last race.
Two significant incidents stood out. At the European Grand Prix, Diniz escaped serious injury when his car was launched into a barrel roll at the start; the roll bar failed during the accident, a concerning outcome given the severity of the impact. Separately, Alesi was hospitalised after a high-speed crash at the Hungaroring.
After Michael Schumacher's serious accident at Silverstone, Sauber were briefly close to losing Alesi to Ferrari as a potential replacement. Alesi declined what was described as a hypothetical offer. Following the Hungarian Grand Prix, Alesi publicly criticised the car and team in an interview and subsequently announced his departure to sign for the Prost team. Mika Salo — who had ultimately stepped in for Schumacher at Ferrari rather than Alesi — signed with Sauber shortly after to fill the vacancy.
At the season's conclusion, Diniz and Alesi placed 14th and 15th respectively in the Drivers' Championship. The team finished eighth in the Constructors' Championship with five points, their lowest haul since entering Formula One in 1993.
The C18's season marked a low point in Sauber's mid-career history, combining reliability failures with a difficult driver situation. The car's development nonetheless kept the team competitive enough to retain its Ferrari engine partnership, which would continue to define the team's technical identity into the following seasons.