The amalgamations in the present municipality took place in 1967 when three rural municipalities joined the City of Oskarshamn, which was transformed into a municipality of unitary type in 1971.

In 1966 construction started on the first nuclear power plant, OKG, within the present municipality. Since then two more reactors have been built and the plant today produces about 10% of Sweden's electricity. Oskarshamn Municipality is today considered to be a possible location of the Swedish nuclear waste storage.

Oskarshamn was named after King Oscar I of Sweden. The top of the coat of arms show the insignia of the King. In the other fields there are symbols for shipping (the anchor), trade (the staff of Mercury) and wealth (the cornucopia).

Its current design stems from 1942, but it basically only differes from the old in the alignment of the symbols. The coat of arms was re-used for the new municipality after 1971 and the arms of Döderhult and Misterhult became obsolete.

There are nine urban areas (also called localities, Swedish: tätorter) in Oskarshamn Municipality.

In the table the localities are listed according to the size of the population as of December 31, 2005. The municipal seat is in bold characters.

1) A minor part of Emsfors is in Mönsterås Municipality

The Swedish Social Democratic Party has been governing the city and later the municipality since 1932, however not always forming an absolute majority. It usually builds a majority with the Left Party of Sweden. All parties that are represented in the Riksdag are also represented in the municipal assembly kommunfullmäktige.

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Wikipedia