Its logos will be seen on the Swiss team's C44 and on the overalls of drivers Valtteri Bottas and Zhou Guanyu at the Miami and Las Vegas GPs, while its parent company Energy Transfer will be featured in Austin.
Sunoco has a long history of involvement in US motorsport and is the official fuel supplier for NASCAR.
It enjoyed an iconic relationship with Roger Penske that saw Mark Donohue win the 1972 Indy 500 and the 1973 CanAm title in the company's blue and yellow colours.
Penske also ran a privateer McLaren M19 in full Sunoco branding at the final two Grands Prix of the 1971 F1 season, with Donohue finishing a remarkable third on his F1 debut in the Canadian GP at Mosport Park.
He was also supposed to compete in the US GP at Watkins Glen the following weekend, but was caught out by a clash with a rain-delayed IndyCar race, and had to cede his seat to David Hobbs.
When Penske entered F1 with his own chassis for Donohue at the end of 1974 his cars carried small Sunoco logos, which were also present when John Watson won the 1976 Austrian GP, the US-owned team's final season.
Sauber, which uses Shell products, has not carried any fuel partner logos thus far this season.
"According to the technical partnership with Ferrari, they supply us not only the power units, but also fuel and lubricants that are developed by Shell, in partnership with Ferrari," team representative Alessandro Alunni Bravi told Motorsport.com.
"Of course, we are entitled to appoint as a team and official partner a sponsor of the team in the fuel and lubricants sector. And we are really happy to start this partnership with Sunoco, that for this year will be limited to the three US Grand Prix.
"Sunoco is a historic brand, very close to motorsport, and they produce race fuels. So I think that their DNA is really linked to motorsport and races."
Alunni Bravi says that the relationship goes beyond logos on the car: "Sunoco is part of a big group, Energy Transfer. We are working together with them at 360 degrees as a partner for the team also in terms of sustainability, and the activations around our sustainability actions.
"They are very proactive in terms of energy storage, and all the products for mobility. So for us both sides are really exciting."
The Sauber team becomes Audi in 2026 and will have its own dedicated fuel/oil supplier, but there is still an opportunity for the Sunoco deal to be extended in the final interim season in 2025.
"As I mentioned, it is a historic brand, but also focussed on and projecting into the future," said Alunni Bravi.
"The aim as always with each partner is to have the possibility to expand our partnership, whether this could mean a seasonal partnership, or to apply the partnership as much as possible and activate as much as possible.
"I think that thanks to the popularity of F1 in the USA to be associated with our team in the US Grands Prix can provide them a very strong platform to increase their brand awareness in the US, but also abroad."
