The incident is one of the most disruptive digital ransom operations ever reported and has prompted calls from American lawmakers to tighten protections for critical US energy infrastructure against hackers.
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 US 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 US Southeast.
While the US government investigation is in the early stages, a former US official and two industry sources said the hackers are likely a professional cybercriminal group and that a group dubbed "DarkSide" was likely among the 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 into respond to the attack, according to the two industry sources. FireEye declined to comment.
Colonial said late on Saturday 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 DarkSideand took nearly 100 gigabytes of data out of Colonial's network on Thursday ahead of the pipeline shutdown.
Colonial did not immediately reply to an email from Reuters seeking comment outside usual US business hours.
Biden briefed on the incident
President Joe Biden was briefed on the incident on Saturday morning, a White House spokesperson 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 US 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 InvestmentsCompany 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 saidtheir operations had not yet been impacted. Some were monitoring developments and working to find alternative transport for customers.