LONDON--Royal Dutch Shell PLC (RDSB.LN) said Thursday it has completed the sale of its 30% interest in Oil Mining Lease 24 in the Eastern Niger Delta to Newcross Exploration and Production Ltd. for $600 million.

The Anglo-Dutch oil major is selling the interest as part of the strategic review of its subsidiary Shell Petroleum Development Company of Nigeria Ltd.'s onshore portfolio, and follows approvals from the relevant authorities of the Federal Government of Nigeria.

Shell's Nigerian subsidiary is the operator of a joint venture between the State-owned National Petroleum Corporation, which owns 55%, Total SA (TOT) of France with 10% and Eni SpA (E) of Italy, which owns 5%.

In June, Shell announced a strategic review of its Niger Delta operations, which it said could result in some divestments, while at the same time announcing that it planned to invest $3.9 billion in other projects onshore in the Delta.

Shell has been in Nigeria for more than 50 years and said it remains committed to keeping a long-term presence there, both onshore and offshore.

OML24 covers an area of some 430 square kilometers and includes the Awoba, Awoba Northwest and Ekulama fields and related facilities. The infrastructure being sold includes three oil-flow stations and three gas-processing plants, in addition to various oil and gas pipelines.

The fields produced on average around 13,000 barrels of oil equivalent per day during the first half of 2014.

Write to Ian Walker at ian.walker@wsj.com; @IanWalk40289749

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