The Canada Energy Regulator has approved preliminary interim tolls for the expanded Trans Mountain pipeline.

The approval will enable Trans Mountain Corp. to begin charging oil shippers once the pipeline expansion, which is still under construction, becomes operational early next year.

The newly approved benchmark fixed toll of $10.88 per barrel means oil companies will be paying nearly twice the amount that Trans Mountain had previously estimated back in 2017.

The company applied to increase the tolls in an effort to recoup some of its costs after the pipeline expansion project's construction costs spiralled to $30.9 billion from a 2017 estimate of $7.4 billion.

The regulator says its preliminary decision is intended to ensure a tolling structure is in place in time for the pipeline's start-up. 

But it says it still plans to complete a more detailed assessment, which will include a formal hearing, of the proposed interim tolls.