May 25 (Reuters) - Nine foreign oil workers were kidnapped from a ship off the coast of Nigeria on Friday, bringing the total number of foreign hostages in the country to 25.

Industry sources said the workers -- three Americans, four Britons, a South African, a Filipino and a Nigerian -- were seized from a pipe laying vessel contracted to Nigerian oil company Conoil.

The raid came a day after gunmen kidnapped a Polish engineer near the oil city of Warri, also in the Niger Delta.

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

-- March 14 - Militants release two Italian workers they had been holding since Dec. 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 Bayelsa. Separately, gunmen abduct a Belarussian woman, who works as a manager of Britain's Compass Group, from outside her home in Port Harcourt's exclusive GRA district. She is freed on May 16.

-- 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 feeding its Brass export terminal. The Movement for the Emancipation of the Niger Delta (MEND) claims 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.

-- May 19 - Two Indian staff of Eleme Petrochemical Company, majority-owned by Indonesia's Indorama, are kidnapped by gunmen in Port Harcourt.

-- May 22 - Four gunmen kidnap a Lebanese man who is a financial controller at oil service company Nigercat in the city of Warri.

-- May 24 - Gunmen kidnap a Polish engineer near Warri.

-- May 25 - Nine oil workers are kidnapped from a ship off the coast of Nigeria; those held are three Americans, four Britons, a South African, and a Filipino.

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