Power was restored to the refinery on Thursday night, BP said on Friday, and workers returned to the plant.
BP was assessing nits, piping and the electrical system for possible damage and to determine the exact cause of the power loss, initially attributed to a transformer failure, the sources said.
Refining analytics firm IIR said it understood that two transformers failed on Thursday.
If no damage is found by the assessments, the refinery could be back to full production by mid-February at the latest, the sources said.
Prices in the Chicago market for gasoline and diesel continued increasing following gains from Thursday after the BP outage.
Ultra-low-sulfur diesel spot prices gained 12 cents to an 18-cent discount to U.S. heating oil futures , while CBOB gasoline increased 12 cents to a 20-cent discount to gasoline futures .
Markets also reacted to news of multiple units shutting down on Thursday night at Phillips 66's (PSX.N), opens new tab 208,000 barrel-per-day Ponca City refinery in Oklahoma during the evening of Feb. 1, Wood Mackenzie said. Two crude distillation units, two fluidic catalytic crackers, a catalytic reformer and a vacuum distillation unit were shut, leading to elevated flaring, Wood Mackenzie added.
All but the most essential workers were evacuated from the plant during the power outage and unplanned shutdown, the sources said.
The two sources said this was the first time they remember a plantwide power outage at the Whiting refinery.
A fire in a single electrical line on Aug. 24, 2022, led to the shutdown of the refinery's cooling water system, causing a full shutdown. The refinery returned to production within a week and a half.
No injuries were reported from the power outage and shutdown, the company said.
