CHRONOLOGY: Nigerian militant attacks on oil industry

(Reuters) - Heavily armed gunmen kidnapped four U.S. oil workers from a barge off the Nigerian coast near Chevron's Escravos crude export terminal on Wednesday, authorities said.

The Movement for the Emancipation of the Niger Delta has forced the shutdown of up to a third of Nigeria's oil capacity. MEND said pipeline attacks on Tuesday were designed to embarrass President Olusegun Obasanjo in his last days in office.

Below is a chronology of some recent major attacks and kidnappings involving the Nigerian oil industry in the last three months.

-- March 8 - A Filipino oil contractor is freed.

-- March 14 - Militants release two Italian workers they had been holding hostage since December 7.

-- April 4 - A Dutch manager for German building contractor Bilfinger Berger, kidnapped in Port Harcourt on March 23, is released. A British worker, abducted from the Bulford Dolphin oil rig on March 31, is freed. Two Lebanese employed by Setraco who were abducted in Bayelsa on April 2 are also released.

-- April 7 - Gunmen kidnap two Turkish engineers from their car in Port Harcourt. One works for Merpa, a Turkish firm that maintains telecommunications on oil platforms.

-- April 27 - Gunmen kill two policemen in a failed kidnap attempt in Port Harcourt as the officers were escorting a convoy of vehicles carrying expatriate staff to work.

-- May 1 - Four Italians are among six oil workers kidnapped from an offshore oil facility operated by U.S.-based Chevron. Chevron reduces output by 15,000 barrels a day.

-- May 3 - Gunmen kidnap 20 foreign workers in three attacks in the Niger Delta but eight are freed within hours. Saipem reduces output by about 50,000 barrels a day.

-- May 5 - Gunmen abduct a British oil worker from Trident 8 rig operated by U.S.-based Transocean off the coast of the state of Bayelsa. Separately, gunmen abduct a Belarussian woman, who works as a manager of Britain's Compass Group, from outside her residence in Port Harcourt's exclusive GRA district.

-- May 8 - Three South Koreans and eight Filipinos are freed after being held for five days.

-- Rebels blow up three oil pipelines in the Niger Delta, forcing Italian oil giant Eni to halt production of 150,000 barrels per day (bpd) feeding its Brass export terminal. MEND claim responsibility.

-- May 9 - Four U.S. oil workers are kidnapped from a barge off the coast near Chevron's Escravos crude export terminal. The barge is operated by U.S. contractor Global Industries.