Oliveira takes his first MotoGP pole at home in Portimao.
Morbidelli and Miller complete the front row, with Crutchlow starting fourth for his final race as a full-time MotoGP rider.
MotoGP is making its Portimao debut with Mir having wrapped up the 2020 title last weekend in Valencia, but six riders still in with a mathematical chance of second in the standings, currently held by Morbidelli.
Suzuki and Ducati are tied at the top of the constructors’ standings, with Yamaha also in title contention, 13 points back. If Suzuki clinch the title it would be for the first time since 1982, Ducati for the second time along with 2007, and Yamaha for the first time since 2015.
There is also the possibility of a record 10th different race winner of the season on Sunday.
Iker Lecuona is being forced to miss his third event after a positive Covid test and is being replaced at Tech3 by KTM test rider Kallio.
Bradl is replacing injured reigning world champion Marc Marquez, who won’t return until 2021.
Official Portimao MotoGP records:
Jack Miller AUS Ducati 1m 39.205s (2020)