Consumers Co-operative Refineries of Saskatoon pleaded guilty to failing to ensure that work was sufficiently and competently supervised.
Occupational Health and Safety laid charges against the Co-op refinery in July 2013.
The department alleged the refinery didn't implement a general corrosion monitoring program, failed to adequately maintain equipment and didn't ensure worker safety.
Four of five charges were withdrawn.
An investigation found that the explosion was caused by a ruptured pipe thinned by corrosion.
Since 2011, there have been four fires at the Regina refinery, including an explosion last Christmas Eve.