The workers, three Britons and two Malaysians, were taken from the compound in Eket on Tuesday, close to the operational base of ExxonMobil, which exports about 800,000 barrels a day from Nigeria, Africa's top oil producer.
The two security guards killed in the raid were believed to be Nigerians, according to sources in the oil industry.
A spokeswoman for ExxonMobil said she had no information about the attack. Earlier reports had indicated that as many as 11 expatriates had been kidnapped.
The abductions come just one day after about 25 Nigerian staff of a Royal Dutch Shell contractor were abducted and at least 10 soldiers were believed to have been killed in a militant raid on a convoy of boats supplying oilfields in a different part of the delta.
About 70 armed men in speed boats attacked the barges carrying fuel and other supplies to Shell facilities in the remote Cawthorne Channel in Rivers state in the delta.
Industry sources said there were two other raids, possibly by the same group, on oil industry boats in the same area, also on Monday, in which one more soldier was killed and several rifles were seized.
The latest attacks come after a period of relative calm in the Niger Delta during September.
The region accounts for all of Nigeria's oil out put, the world's eighth biggest exporter.
One sixth of Nigeria's production capacity has been shut down since February following a wave of militant attacks on oil facilities that month.
The militant group behind February's attacks, the Movement for the Emancipation of the Niger Delta, said it was not involved in Monday's raids.
However, in a statement on Tuesday, it said it had moved fighters into Rivers state to defend communities from reprisal attacks by the military.
Violence in the delta is a result of widespread poverty, corruption and lawlessness.
Most inhabitants of the wetlands region have seen few benefits from five decades of oil extraction that has damaged their environment.