Williams will head to Spain with a "few upgrades" that Felipe Massa are hoping will ensure Williams closes the gap to those ahead.
Although Williams were the second best team out on track in the latter stages of last year's Championship, they have fallen behind Ferrari this season.
The Scuderia have been the ones to take the fight to Mercedes with one Ferrari joining the Brackley team-mates on the podium in each of the opening four races.
Massa, though, is hoping Williams can pull one back this weekend at Barcelona.
"We've completed two weeks of testing in Barcelona over the winter so we know how our car can perform around the circuit and are probably more prepared for this race than any other race on the calendar," said the Brazilian.
"We have shown in the first few races that we have a good car and a few upgrades will be appearing in Spain that we need to make the most of if we are going to close the gap to the cars in front.
"It's good to be back in Europe and I hope we can start this part of the season with a strong result."
Meanwhile, Rob Smedley, the team's head of vehicle performance, will be a good measure on how much progress Williams have made since pre-season testing.
"We're heading into the European season after a reasonably successful campaign that has put us a solid third position in the championship. Our aim now is to keep moving forward and close the gap to the teams in front.
"Barcelona is a good measure of everyone's upgrade packages and shows how well teams have developed their cars. The circuit is an excellent test of a Formula One car with Turn 3 offering a long, high speed test and sector three always being demanding on the car as it exposes its performance levels.
"We are heading into the weekend with a lot of confidence but there will be a lot of work to do leading up to qualifying as we learn about the new updated package."