Motiva has started up the new crude distillation unit (CDU) at its massive refinery in Port Arthur, Texas, according to Simon Henry, chief financial officer of Motiva partner Royal Dutch Shell.

Motiva is a 50-50 joint venture between Shell and Saudi Arabia's state-run oil company Saudi Aramco.

The startup is among the finishing touches on a 5-year expansion project that cost approximately $7 billion.

The crude distillation unit is now processing oil and the hydrocracker is expected online by the end of the second quarter, Henry said on a Thursday conference call with reporters.

The 325,000 bpd atmospheric crude distillation unit that started processing is combining with existing units to raise capacity to 600,000 bpd, making the Motiva refinery the largest in the US.

It could take until the third quarter of this year for refinery rates to hit capacity.

With the Motiva expansion, the ExxonMobil refinery in Baytown, Texas, drops to the second-largest in the US. It has a reported capacity of 560,640 bpd.