Colonial moves 2.5 million barrels per day of gasoline and other fuels from refiners on the Gulf Coast to consumers in the mid-Atlantic and southeastern United States.
Its 5,000 mile (8,850 km) network serves major U.S. airports, including Atlanta's Hartsfield Jackson Airport, the world's busiest by passenger traffic.
Retail fuel experts including the American Automobile Association said an outage lasting several days could have significant impacts on regional fuel supplies, particularly in the U.S. Southeast.
While the U.S. government investigation is in the early stages, a former U.S. official and two industry sources said the hackers are likely a professional cybercriminal group and that a group dubbed "DarkSide" was among potential suspects.
DarkSide is known for deploying ransomware and extorting victims while avoiding targets in post-Soviet states. Ransomware is a type of malware designed to lock down systems by encrypting data and demanding payment to regain access.
Cybersecurity firm FireEye has also been brought in to respond to the attack, according to the two industry sources. FireEye declined to comment.
Colonial has said it was working with a "leading, third-party cybersecurity firm," but did not name the firm.
Bloomberg News, citing people familiar with the matter, reported late on Saturday that the hackers are part of DarkSide and took nearly 100 gigabytes of data out of Colonial's network on Thursday ahead of the pipeline shutdown.
Messages left with the DarkSide hackers were not immediately returned. The group's dark web site where hackers regularly post data about victims made no reference to Colonial Pipeline.
BIDEN BRIEFED ON HACK
President Joe Biden was briefed on the cyberattack on Saturday morning, the White House said, adding that the government was working to try to help the company restore operations and prevent supply disruptions.
Another fuel pipeline serving the same regions carries a third of what Colonial does. Any prolonged outage would require tankers to transport fuels from the U.S. Gulf Coast to East Coast ports.
The privately held, Georgia-based company is owned by CDPQ Colonial Partners L.P., IFM (US) Colonial Pipeline 2 LLC, KKR-Keats Pipeline Investors L.P., Koch Capital Investments Company LLC and Shell Midstream Operating LLC.
Gasoline futures and diesel futures on the New York Mercantile Exchange rose on Friday after the outage was reported. In previous Colonial outages, retail prices have risen substantially, if briefly.
Oil refining companies contacted by Reuters on Saturday said their operations had not yet been impacted. Some were monitoring developments and working to find alternative transport for customers.
(Writing by Richard Valdmanis Editing by Frances Kerry and Grant McCool) ((firstname.lastname@example.org; +1 617 312 6022;))