The United States government has offered a bounty of up to $10million (£7.4m) for information about the hacking group known as DarkSide.
In May, a DarkSide ransomware attack shut down a vital 5,500-mile-long fuel pipeline on the east coast of the US.
The pipeline carries 45% of the fuel used on the east coast.
The bounty is offered for information which can lead to the "identification or location of any individuals" in a leadership position with DarkSide.
A separate $5m reward has been offered for information leading to the arrest of anybody "conspiring to participate" in a DarkSide ransomware attack.
The cyber-attack caused fuel shortages after the Colonial Pipeline company shut down its operations for several days.
It eventually paid the $4.4m ransom in Bitcoin.
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Crypto-currency analysis company Elliptic estimated that DarkSide had received at least $90m in ransom payments from 47 victims.
However, US authorities later said 63.7 Bitcoin, the majority of the ransom paid by Colonial Pipeline, had been recovered.
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