Jonathan Rea topped the timesheets at the first free practice on Friday morning at Motorsport Aragon.
The Kawasaki rider continued his perfect start to the 2017 season with a flying 1:50.570s around the Spanish circuit. The Northern Irishman has been unchallenged, winning each of the four races so far this year.
Pata Yamaha rider Alex Lowes was a close second behind Rea, with a 0.071s gap between the two.
A further 0.158s behind Read was third fastest Xavi Flores of BARNI Racing team, who took advantage of the clearing conditions near the end of FP1.
Flores is followed by fellow Spaniard Jordi Torres and Tom Sykes , with Michael van der Mark rounding out the top six.
Warmer conditions are predicted for the second free practice, so the riders are expecting to improve on their times.