Pirelli test tyres in use
Teams and drivers are also testing out Pirelli's new tyres that are coming into use at the British GP next month.
Two additional sets of the new Pirelli hard tyre will be available to test in this session and Practice Two later on.
Pirelli will introduce a new tougher specification of tyre at the British Grand Prix to cope with "extraordinary" advances in car performance.
Far higher than expected downforce levels have prompted a change, with a pole position time that was two seconds faster than last year at the Miami Grand Prix having highlighted the issue.
Plenty of drivers are setting their early lap times on the test tyre, including the two Red Bulls at the top of the timesheet.