Commander Pablo, a representative of the ELN (National Liberation Army in English), told reporters that Occidental Petroleum from the US, Spanish-Argentine combine Repsol-YPF and Colombia's own Ecopetrol were now targets.
The group, he said, reading from a communique, would now resume bombing a oil pipeline the three operate.
The pipeline is the Cano Limon, the second largest in Colombia with a capacity of 120,000 barrels a day. It was bombed a record 170 times last year - by the bigger FARC guerrillas as well as the ELN.
The group is also protesting at $89m in aid included in President George W Bush's proposed 2003 US budget, to train and outfit troops to protect the pipeline.
Decades of war
The 38-year-old civil war in Colombia has claimed at least 40,000 lives since the beginning of the 1990s.
The ELN called off a truce with the government at the beginning of this year, accusing the government of bad faith and returning to war both with the national armed forces and with right-wing paramilitaries who are at least as feared, if not more so, than the left-wing rebels.
The ELN itself was formed in the 1960s by Colombians inspired by the socialist Cuban revolution of the late 1950s.
Both groups make much of their money out of kidnapping and extortion, often involving the oil industry.
But the ELN is distinguished from the FARC in part because it splits its efforts between military and social work, and its refusal to become involved in the narcotics trade.