Williams has announced a "long-term" engine deal with Mercedes, beginning in 2014.
The great British team is currently powered by Renault's V8 engine, but - as F1 switches to new regulations at the end of the season - the French marque is charging more than Mercedes and Ferrari for its turbo V6.
"Williams will continue to manufacture its own transmission," the team said in a statement.
"This new agreement provides Mercedes-Benz with the long-term stability of supplying our works team and at least two partners from the 2015 season onwards, following the conclusion of our relationship with McLaren at the end of next season," said Mercedes' engine managing director, Andy Cowell.
The other Mercedes-powered F1 team is Force India.
For its part, Renault has indicated it can cope with the loss of F1 engine customer Williams.
Amid reports Mercedes is offering its turbo V6 at a lower price, Williams announced that it is switching from Renault to the German marque for 2014 and beyond.
Renault, currently also supplying Red Bull, Lotus and Caterham and adding Toro Rosso to its roster for 2014, said the idea of five customers in 2014 "would not make sense economically or be ideal for our resources".
"Three or up to four teams is the ideal for us so the departure of Williams normalises the situation and makes things much clearer from our side," said Renault Sport F1 president Jean-Michel Jalinier.
Caterham is expected to stay with Renault in 2014, but it has been reported that Lotus is in talks with Ferrari.
Jalinier said: "We will announce the next team within a matter of days, and then confirm the final stage before the end of June."
Wolff not talking about 'secret test' consequences
Mercedes director and team co-owner Toto Wolff is refusing to say he is worried about potential penalties as a result of the secret Pirelli tyre test.
Although Jenson Button said he senses a "slapped wrist" might be the outcome, Red Bull's Dr Helmut Marko likened the affair to 'spygate', where McLaren was excluded from the constructors' championship in 2007 and fined $100m.
"I think it's not up to us to talk about sanctions or to express concerns," Wolff told DPA news agency.
"It will be a controlled process, and we respect the authority of the FIA. Everything is run very professionally and transparently, and so I have great confidence in the process," he added.
Red Bull and Ferrari were the only teams to formally protest the Mercedes test, but it is believed most other rival bosses have a similar view.
"They all say 'We're behind you'," said a cynical Christian Horner. "Just four miles back."
But Eric Boullier, boss of the Lotus team, said he is concerned that notwithstanding Pirelli's contract with the FIA, Mercedes broke the sporting regulations.
"There is a sporting regulation in place, there is even a testing agreement in place between the teams," he is quoted by the Sun newspaper.
Marussia's Graeme Lowdon agreed: "My understanding is we're not allowed to test in season and from what I understand, that was an in-season test.
"I'm sure it will be investigated with the vigour required."
Mika Salo, a former Ferrari and Sauber driver and an occasional FIA steward, thinks teams are angry because of the 'secret' nature of the Barcelona test.
"Paul Hembery did hours of press conferences on Thursday and Friday and he didn't mention the test -- actually he complained that developing tyres is so difficult for Pirelli because there is no testing," Salo told the Finnish broadcaster MTV3.
"He forgot to mention that he had just done three days with Mercedes."
Gerhard Berger thinks both Pirelli and Mercedes are to blame.
"I would not excuse Pirelli," he told Servus TV. "But if Pirelli has failed to clarify something, it is up to Mercedes to really make sure it was clarified."
There is now speculation the 'secret test' affair could cost Pirelli its place in formula one.
Red Bull's Christian Horner is quoted by EFE news agency: "They are a competent company.
"Yes, they have pushed the boundaries with its products a little, but the problem is not Pirelli, but the way all of this has happened, the lack of transparency."
Report links Ford with F1 return
German-language publication Speed Week has named Ford as a potential candidate to return to formula one after the new V6 rules debut in 2014.
Honda, having pulled out at the end of 2008, has already announced its return with McLaren in 2015, but Toyota and BMW have denied speculation they are also tempted by the sport's incoming, automobile industry-relevant engine rules.
Speed Week, however, is now mentioning Ford.
Ford bought Sir Jackie Stewart's team in 1999, rebranding it Jaguar Racing, but pulling out of F1 at the end of 2004.
The Milton Keynes based team was subsequently sold to current champions Red Bull.
Hamilton identifies brakes as main problem
Lewis Hamilton's main problem as he grapples to get up to speed with Mercedes teammate Nico Rosberg is the W04 car's brakes, it has emerged.
Beaten to pole position by Rosberg on the last three outings, Hamilton departed Monaco last Sunday - having watched the sister car stroll to victory - vowing to get his "s--- together".
He is quoted by France's L'Equipe as admitting that the biggest difference between his new Mercedes and his McLarens of past seasons are the brakes.
"At McLaren, I had 100 per cent confidence in the car, and I'm working to regain that confidence," said the 2008 world champion.
"The setup and the brakes are very different to what I was used to," added Hamilton.
"It's an overall feeling that's hard to explain. It's not a problem of concentration, it's just confidence in the car," he said.
F1 'no place for Grosjean to practice' - Salo
Romain Grosjean's days in F1 could be numbered, according to former driver and Finnish pundit Mika Salo.
Having apparently put his 'first lap nutcase' troubles of 2012 behind him, the Frenchman was back in the wars in Monaco, crashing no fewer than four times.
He will have to move ten places down the grid in Canada due to the crash with Daniel Ricciardo, reinvigorating reports his days at Lotus are numbered.
"It's hard to say what Lotus will decide, but he is causing a lot of damage and losing a lot of points, which is not what the team needs financially," Salo told MTV3.
"Soon, he will hurt someone else or himself," the former Sauber driver warned.
"Grosjean is incredibly fast, but too prone to error for this series. He's had enough years to practice, but there comes a time that this is not the place to practice anymore."
Also under the microscope after Monaco is Sergio Perez, whose controversial driving attracted the ire of prominent rivals like Fernando Alonso, Kimi Raikkonen and even his own McLaren teammate Jenson Button.
Jean-Eric Vergne, the Toro Rosso driver, was also unimpressed.
"To be honest, I get no pleasure from the misfortune of other drivers, because it's also happened to me," the Frenchman is quoted by Auto Hebdo.
"But if I did have a comment, I would say that Sergio has not had bad luck, I think he went out (of the race) because he wanted to. Or at least he seemed to try his best.
"I think the word bad luck is more applicable to Daniel (Ricciardo), when Romain (Grosjean) crashed into him!"
Domenicali, Alonso tip Ferrari to bounce back
Stefano Domenicali has tipped Ferrari to bounce back in Canada next weekend.
Off the back of his Barcelona win, Fernando Alonso struggled in the Principality last weekend, qualifying sixth and finishing just seventh.
It was a blow for the Spaniard in the drivers' championship, who is now almost 30 points behind Sebastian Vettel.
"From the sporting point of view," team boss Domenicali is quoted by Brazil's Agencia Estado, "the only positive was Kimi Raikkonen failing to score many points, but Vettel was second.
"Anyway, we have only had 6 races out of 19 -- the championship is very long."
Indeed, Ferrari rarely shines in Monaco, with the Maranello team failing to win a race on the glamorous streets since Michael Schumacher in 2001.
"Unfortunately, there must be a reason for that; perhaps it's the characteristics or something else, I don't know," said Domenicali.
"But in this race we had no pace and we have to find out why, because we are used to reacting quickly after a difficult weekend."
Alonso is also looking ahead to Canada, where he expects things to return to "normal" for Ferrari.
"It is a lower downforce circuit so I'm convinced that we'll be in better shape and fighting for good points," he is quoted by Spain's Diario Sport.