Williams driver Valtteri Bottas says he is hopeful that the outfit can fight with Ferrari and Red Bull in 2016, but concedes it is unlikely Mercedes will be caught.
Bottas finished the opening day of the second test in second position, 0.207s behind Nico Rosberg, albeit having set his best time on the Ultra Soft tyres compared to the Softs utilised by the German driver.
Williams has finished third in the Constructors' championship for the last two years, having beaten Ferrari in 2014 and Red Bull in 2015, leaving the Finn to eye a fight between those two operations.
"I have one day left [in testing] so what I have so far is progression from last year and what I said before it’s so difficult in fine detail to say where we are, Mercedes looking strong but I hope we can fight with Ferrari and Red Bull," he explained.
"At the moment it looks like they’re [Mercedes] in a really strong position and where we are now it’s quite tricky for anyone to challenge them at the beginning of the season.
"That is the fact at the moment but let’s see, I sure we’ll still progress a lot from these tests and we know there’s plenty more to come."