Who holds the key to F1's 2018 driver market?

There is no such thing as a sure thing in Formula 1. You can only play the percentages. Particularly when it comes to the driver market. Even solid contracts can be broken, if the will is there. Just ask Mercedes and Nico Rosberg.

Basing your career progression on random sequences of events outside of your control is anathema to most in a world where science and logic rule. But even an environment that tries to control events to the nth degree still gets turned upside down by changes of heart, an unexpected triumph of emotion over rationality, or plain old dumb luck.

Valtteri Bottas must have thought he'd missed his shot at the big time when a potential deal to join Ferrari for 2016 fell through. But he stayed with Williams for another year, was set to stay for one more after a brief flirtation with Renault, and now he's suddenly a double grand prix winner with Mercedes, thanks to events set in motion by Rosberg's unexpected retirement last December.

Everyone thought Fernando Alonso would be a Ferrari driver in 2015. He had a contract - until the end of '16 apparently - but negotiations to extend it broke down during 2014, Sebastian Vettel found a way out of his existing Red Bull deal and into Maranello, and three years later Vettel is gunning for a fifth world championship with the Prancing Horse while Alonso toils with the never-ending nightmare that is McLaren-Honda.

Alonso is back on the market this year, a free agent for 2018. He's made the world very aware of his dissatisfaction with the current competitive standing of the McLaren-Honda project, and thus his potential availability to rival suitors.

Current championship leader Vettel also needs to negotiate a fresh contract for 2018, as does his Ferrari team-mate Kimi Raikkonen, as does Bottas for that matter. With Lewis Hamilton, Daniel Ricciardo and Max Verstappen all locked in to arrangements - with Mercedes and Red Bull respectively - that don't expire for at least another term, all eyes are on what Mercedes will do with Bottas, what Ferrari will do about Vettel and Raikkonen, and where Alonso might fit into this picture.

Barring an unexpected turn of events, of the kind that put him in post in the first place, it's difficult to see Bottas not remaining at Mercedes for a second season.

It's a dream opportunity for him, he's arguably out-performed expectations over the first nine races, Hamilton and Mercedes are much happier with the current intra-team dynamic than the previous one, and the team will surely be desperate to avoid a repeat of the sort of destabilisation that made last winter so difficult. It seems just a matter of time before Bottas's contract is renewed.

That would rule out a move to Mercedes for Alonso, whatever his former manager Flavio Briatore - photographed having dinner with Mercedes senior management in Baku - might dare to dream for the driver he calls F1's answer to Lionel Messi.

A return to Ferrari also looks unlikely while Sergio Marchionne, newly president when Alonso left the team in 2014, still rules the roost. "We are not interested," was Marchionne's response to questions about Alonso at the Austrian Grand Prix.

Ferrari has no obvious reason to ditch Vettel, who is performing very well this season - Baku histrionics aide - and leading the world championship comfortably. Equally, Vettel has no obvious reason to depart Maranello while things are going so well.

The future of team-mate Raikkonen is the never-ending story of recent F1 'silly seasons'. Marchionne's recent comments about Raikkonen being an occasional "laggard" in races will put Maranello hopefuls on red alert, but that could well be merely a motivational tactic similar to that employed by team principal Maurizio Arrivabene early last season.

Like Mercedes, Ferrari will be wary of unnecessary disruption. Vettel and Raikkonen work well together, Raikkonen is arguably performing better than at any time since his return to Maranello in 2014 - don't forget he was on pole in Monaco - and all-important team harmony and unity will be maintained by continuity.

That would undoubtedly lead to a collective groan among younger hungry drivers in the paddock, plus observers frustrated by Raikkonen's continued occupation of such a coveted seat. They will point to recent races in Canada and Austria as evidence Raikkonen is too often failing to get the most from a car that fights for victory at most circuits.

But Ferrari is a conservative team and but for a couple of incidents outside of his control, Raikkonen would have at least 30 more points to his name - enough to equal out the constructors' championship fight and put Raikkonen about the same number of points behind Bottas by which Hamilton trails Vettel in the drivers' championship at this stage.

Raikkonen should also by rights have many more points than at this same stage last season, when Ferrari decided - against the expectations of many - to renew terms with the 2007 world champion for another year. There is every chance this could happen again.

If not - all bets are off. Ricciardo, Verstappen and Carlos Sainz Jr are often linked with moves to Maranello, though of that Red Bull-contracted group only Ricciardo fits the Scuderia's typical age profile (25 years plus) for a driver.

It's interesting that Red Bull felt compelled to activate the option in Sainz's rolling contract for another year ahead of the Austrian GP, plus clarify that team-mate Daniil Kvyat is likely to be retained and state publicly that Verstappen is signed to Red Bull until the end of 2019.

Although he was admonished by Red Bull bosses Christian Horner and Helmut Marko for speaking out in Austria, Sainz was right to suggest a fourth season at Toro Rosso in 2018 would be "unlikely" - in fact, unprecedented.

But Red Bull does not appear to enjoy the same strength in depth in its young driver programme that it has counted on previously.

Pierre Gasly was not convincing enough while winning last year's GP2 title to earn promotion, Formula 2 racer Sergio Sette Camara was dropped, Niko Kari is having a difficult time in GP3, and the others on the programme this year - Dan Ticktum, Neil Verhagen and Richard Verschoor - are promising talents much earlier in their careers, and not dominating Formula Renault in a way that suggests they are about to make a Raikkonen-like leap into the big time.

So, Red Bull needs insurance in the driver market. Sainz and Kvyat provide that insurance, though action on Sainz was particularly pressing for Red Bull given the Spaniard has been courted previously by Renault and is known to be on the radar of other rival teams for '18. Taking up Sainz's option ensures Red Bull must receive compensation should he decide his future lies elsewhere.

Sergio Perez negotiated a one-year extension to his Force India contract for 2017, which many felt was a deliberate tactic to put himself in the frame for Raikkonen's Ferrari seat for '18, while Romain Grosjean is under contract at Haas but the American team won't stand in his way should Ferrari come calling.

Ferrari also has Sauber super-sub Antonio Giovinazzi on its books as third driver this year, plus F2 superstar Charles Leclerc waiting in its Driver Academy wings. Not since the Scuderia signed Gilles Villeneuve at the tail end of the 1977 season (after a single race for McLaren) has Ferrari taken a chance on a driver with such little F1 experience as Giovinazzi. Unlikely, but not unprecedented.

One driver definitely ruled out by Ferrari is Alonso, who it seems must pin his hopes on a McLaren turnaround or quit F1 altogether. Anything else would represent a step backwards for a driver who has arguably been the outstanding performer on the grid so far this season, yet cannot automatically command a seat in any of the top three teams.

Alonso and Briatore may yet get their hands on a Mercedes of some sort - in the form of a customer engine supply deal for McLaren in 2018, in which case there would surely be no hesitation from Alonso in re-signing. The stuttering progress of the Honda engine is the only reason to leave a team that has gradually moulded itself around the double world champion since his 2015 return.

But resolution of Alonso's situation depends first on resolution of McLaren-Honda's - obvious and clear delivery on promises of better to come in the very near future from Honda, or some kind of divorce and compensation package for McLaren. A switch to Ferrari or Mercedes customer engines would not come cheap one imagines, and neither would Alonso's salary for that matter.

If everything plays out this way, the market starts to look choked off again at the top end. That would leave no seats free at any of the top teams and, so long as he arrests his admittedly worrying early slump, there's little reason to expect Stoffel Vandoorne - tied down to a long-term deal with McLaren - won't remain Alonso's team-mate next year should the Spaniard agree fresh terms.

A lack of movement at the biggest teams would create added pressure in the midfield, where several drivers are on one-year tickets and need to impress to secure their futures.

Nico Hulkenberg (Renault), Esteban Ocon (Force India) and Kevin Magnussen (Haas, which expects to retain both of its current drivers) all signed multi-year deals when they switched teams at the end of last season. All are performing well too, so have no reason to not remain in post next year.

Rookie Lance Stroll's agreement is also for multiple seasons (and lucrative for Williams), so there is no reason to expect him to move on in 2018 either. The identity of his future team-mate is less clear. Unless further funding is forthcoming, it's likely Williams will look to a budgeted driver for next season, which would preclude Felipe Massa extending his unexpected comeback into a second season at Grove.

Williams also needs to employ a driver over the age of 25 to satisfy commitments to title sponsor Martini, which rules out a move for drivers such as Sainz, Kvyat and Pascal Wehrlein.

Perez would surely be prime on the list of potential Williams targets, having been honed into one of F1's best midfield operators over recent seasons at Force India, while also bringing an attractive sponsorship package with him. Marcus Ericsson also has to be considered, on account of his commercial backing.

Perez must be a serious consideration for Renault too. The French manufacturer courted him last season, before eventually signing his then-Force India team-mate Nico Hulkenberg. The two work well together, and with Ocon (contracted to Force India until the end of 2019) already showing the capability to disrupt Perez's equilibrium at Force India, Perez may decide remaining at Force India (the team's preferred option) for a fifth season is a stretch too far - even if Ferrari fails to come calling.

Force India is now better prepared for such an eventuality, able to count on the driving prowess of Ocon regardless, plus improved financial stability owing to strong results over the past three seasons and this year's major sponsorship deal with BWT.

Whether or not Renault moves for Perez, it seems unlikely that incumbent Jolyon Palmer will earn an extension to his current deal.

His confidence has taken a battering from a difficult start to the year amid Hulkenberg's strong form, and it's difficult to foresee a way back for him now, unless his own lot dramatically improves through the second half of the season and Renault runs out of alternative options. Rumours continue to swirl suggesting Palmer may even be replaced before this season is through.

That is mainly because of romantic notions of a Robert Kubica comeback, which seem (sadly) a little far-fetched to me.

His exploratory testing with Renault is an evocative reminder of what might have been for one of his generation's top talents, but does Kubica really possess the strength and dexterity to drive a modern F1 car through a gruelling season on all types of circuit? More crucially, can he perform mundane tasks such as extracting himself from the cockpit quickly enough to satisfy FIA-mandated safety criteria?

I fear it is this sort of detail that will unfortunately scupper the dream. But if Kubica can truly prove his capability, why not take the risk? A Hulkenberg/Kubica line-up at Renault would be a real force to be reckoned with.

It's anyone's guess what will happen at Sauber next season. The Monisha Kaltenborn-brokered deal to run Honda engines in 2018 appears to have hit the skids, which would preclude promotion for a Honda junior driver, something that appeared likely when Kaltenborn announced the arrangement.

If the deal is somehow salvaged, then expect a 'Marcus Ericsson plus Honda driver' line-up for next season, provided Ericsson doesn't move on. If not, a lot will depend on which engine Sauber ends up with.

The acrimonious nature of new team boss Frederic Vasseur's departure from Renault at the end of last year suggests that's one option Sauber probably won't look to, but it cannot be ruled out completely.

If Mercedes steps in then Pascal Wehrlein will be almost guaranteed another season in F1, though he would also be a serious contender for a seat at Force India should Perez move on. Renewing terms with Ferrari and upgrading to current engines would surely open the door for Giovinazzi or Leclerc, but leave Wehrlein vulnerable.

There is a lot of congestion in the market, which will only ease once Ferrari decides Raikkonen's future again, McLaren (and Sauber) confirm their engine plans for 2018, Renault decides what more, if anything, to do with Kubica, and Alonso makes his next move. Alonso has previously said he will deliberate his future during F1's August break. In Austria, he said he will decide his future in October.

So F1 must wait patiently, while also preparing for the unexpected. Red Bull has made the firmest moves recently to quell speculation about its future driver line-ups, but no agreement can force a driver race for a team if that driver doesn't want to.

Rosberg had a two-year contract in his pocket when he decided to walk away at the end of the last season, which proves once again, in case anyone needed reminding, that anything can happen in Formula 1 - especially when it comes to something as volatile as the driver market.