"They regained their freedom this morning. The government was able to secure their release without paying any ransom. The project will continue," a Bayelsa government spokesman said.
The Briton was abducted on March 31 by armed men in two speedboats during a pre-dawn raid on the Bulford Dolphin oil drilling rig, 40 miles offshore.
"I can confirm that he has been released. He is in good health as far as we know. He is due to see a doctor and I believe he will be on his way to Lagos," a spokesman for the British high commission in Abuja said.
The Dutch security manager working for German building contractor, Bilfinger & Berger, was seized on March 23 after a three-hour gunfight when men in three speedboats stormed a construction yard in Port Harcourt.
Two security experts working for foreign oil majors said the Dutchman had now been released. One source said the Briton and the Dutchman were freed at the same time, but this could not be confirmed.
Poverty and frustration
Sources said armed groups from the same coastal communities were involved in the abductions of the Briton and the Dutchman, which would explain why they were released on the same morning.
There was no apparent link with the release of the Lebanese.
Security sources said the Briton's kidnappers had previously been in disputes with the operators of the Bulford rig.
Attacks on oil facilities and kidnappings of foreign workers have been a problem in the Niger Delta for years, but the violence has intensified since late 2005.
Oil production has been down by 500,000 barrels a day since February last year because of a series of raids on Royal Dutch Shell oilfields that month by the Movement for the Emancipation of the Niger Delta.
The group has taken hostages to press its demands for greater local control of oil revenues, though all have now been released.
Numerous other "freelance" kidnappers have taken advantage of a breakdown in law and order to seize foreigners and extract ransoms from companies or local governments.
Violence in the delta is rooted in poverty and frustration at the lack of benefits for local people from 50 years of oil extraction that has polluted the air and water of the delta.
Millions of villagers with no access to clean water, electricity or roads resent the multi-billion-dollar oil industry and its web of pipelines criss-crossing their lands.