Colonial Pipeline, the biggest fuel pipeline in the United States resumed operations on Wednesday evening after a five-day closure.
A ransomware cyber-attack forced the company to shut down the main part of its network on Friday.
The 8,900km pipeline usually carries 2.5 million barrels a day on the East Coast.
The closure saw supplies tighten across the US, with prices rising and a number of states declaring an emergency.
However, Colonial Pipeline warned in a press release that it could take several days for the delivery supply chain to return to normal
“Some markets served by Colonial Pipeline may experience, or continue to experience, intermittent service interruptions during the start-up period,” they added in a statement.
The FBI has accused a criminal gang called DarkSide of being behind the ransomware attack.
Colonial had earlier said it will not pay the ransom demanded by the hackers.
Meanwhile, petrol prices soared in several states. The average price per gallon hit $3.008, the highest since October 2014.
Governors in several states — Florida, Virginia, North Carolina and Georgia — declared states of emergency, which mean they can introduce temporary rules to ease prices in their areas as a result.
CENTRAL SYSTEM HACK
Colonial Pipeline’s operations are mostly extremely digital. Pressure sensors, thermostats, valves and pumps are used to monitor and control the flow of diesel, petrol and jet fuel across hundreds of miles of piping.
All this operational technology is connected to a central system where there is a risk of cyber-attack.
According to data collated by tracking firm GasBuddy, at least 3,500 petrol stations had run dry across Virginia, North Carolina and and several other states on Wednesday.
Virginia and Georgia were among the worst-affected, with more than 40% of petrol stations it monitors suffering from outages, it said on its website. In North Carolina, 65% of petrol stations had fuel outages.