Logistical constraints at the Port of Vancouver mean waterborne oil exports from the highly anticipated Trans Mountain pipeline expansion (TMX) may only be around half what the Canadian government-owned corporation has forecast, traders and shipping sources said.

After 12 years and 34 billion Canadian dollars ($25 billion), the project to nearly triple the flow of crude from landlocked Alberta to Canada's Pacific Coast to 890,000 barrels per day began commercial operations on Wednesday after regulatory delays and construction setbacks.

The extra 590,000 bpd of oil will be delivered to the Westridge Marine Terminal, where it can be loaded onto tankers, giving Canadian producers more access to U.S. West Coast and Asian markets.