RCMP say a Chevrolet truck veered off a curve while driving in wet conditions on gravel on Princeton Avenue, shortly before 11 p.m. PT.
The truck spun and rolled before landing upside down, said Kelowna RCMP Const. Kris Clark.
"It appears that a pick up truck came around a corner and lost control on the washboard, gravel road and overturned several time ejecting the occupants of the vehicle."
The driver, Mike Baxter, 20, of Peachland and a 17-year-old former student of Mount Boucherie Senior Secondary School in West Kelowna were pronounced dead at the scene.
Two others, a 19-year-old from Peachland and a 16-year-old from West Kelowna suffered serious, potentially life-threatening injuries. They were rushed to hospital and remain in serious to critical condition.
RCMP say they don't yet know the cause of the crash but Sgt. Brian Nightingale said speed, weather and road conditions may have been factors.
Attended Mount Boucherie Senior Secondary
At least three of the four people in the crash were students at, or had graduated from, Mount Boucherie Senior Secondary School.
School District 23 superintendent Hugh Gloster said a critical response team will be at school on Monday to help students and teachers deal with the tragedy.
"They will provide you know an appropriate response in terms of supporting not just the students themselves, but obviously other members of that school community that could be very closely connected to the victims," he said.
Students at Mount Boucherie have had to deal with a number of tragedies in recent years, including the death of Ashley Hyatt, who was killed at a house party in Peachland in 2010.
The trial for the teen accused in her death begins next week.