It follows a fire and explosion on Dec. 24 that rattled the city.
No one was injured.
The refinery normally produces 130,000 barrels, but reduced that level to 60,000 after the explosion.
Co-Op spokesman Daryl Oshanek says it's unknown when the refinery will be back to full production.
"It's going to be a process yet that's going to take some months and it's going to be difficult to give any estimates as to when we can get back in there, do the cleanup and restore the damaged equipment."
He also says higher production means its stations across the West won't be facing any fuel shortages.
"It's fair to say getting to that 90,000 barrels per day level now means that we see that we do have secured supplies for our Co-Operative retail service stations across Western Canada."
Oshanek says fire investigators are still working to figure out why the fire and explosion happened.
"We cannot go in there and really do anything with the damaged equipment until they do their investigation," he said.
The blast could be heard and felt all over Regina and outside the city as well.
It was the fourth fire in about two years at the refinery.
In February, a fire in a coker unit sent flames shooting nearly 20 metres in the air, but was quickly brought under control.
In October 2011, corrosion in a pipe triggered a fireball that sent seven contract workers to hospital and forced 1,400 workers from the facility. No one was injured.
In May 2012, a much smaller fire occurred when an overheated crude oil pump ignited. There were no injuries.