Maverick Vinales momentarily went top before being replaced by Brad Binder. It's a time of 1:40.689s for the South African.
Brad Binder moves up to fifth spot before making a mistake on his next lap which was set to be even faster.
Marc Marquez goes top again as he becomes the first rider to break into the 1m 40s barrier.
But he's quickly replaced by Oliveira who narrowly moves ahead of the Gresini Ducati rider.
Marc Marquez goes quickest by three tenths with just 15 minutes remaining.
1:41.724s from Miller as he goes quickest once again for KTM.
The leaderboard is continuing to change as impressive rookie Pedro Acosta is now quickest.
Ducati's big guns are beginning to show their pace as Bagnaia goes third and Marc Marquez fourth.
Good early pace from Alex Rins who has gone quickest aboard his factory Yamaha machine.
Oliveira runs off circuit at turn one, highlighting just how dirty the track is at the moment.
Jack Miller is the early pacesetter for KTM, ahead of home favourite Miguel Oliveira.
FP1 is underway at Portimao!
Francesco Bagnaia will be looking to continue his stunning form at Portimao, after the factory Ducati rider won both races in 2023.
Good morning and welcome to day-one of the Portimao MotoGP. FP1 in the premier class is coming up at 10:45 UK time.