South Africa and Mozambique have agreed to join forces to fight piracy off Mozambique's 2,470km-long (about 1,530 miles) coastline.
The two countries' defence ministers signed a deal in Pretoria to set up joint patrols along the coast.
An estimated 30% of the world's oil trade passes through the region and 98% of South Africa's maritime trade.
Piracy in the Indian Ocean has been on the increase as pirates seek to avoid naval patrols off Somalia.
The country has been wracked by constant war for more than 20 years, and its weak transitional government is backed by a 9,000-strong Africa Union peacekeeping force.
After signing the deal, South Africa's Defence Minister Lindiwe Sisulu told journalists her department planned to lobby the international community to strengthen the AU mission in Somalia.
She said as well as joint patrols South Africa and Mozambique would conduct joint training and share information to fight pirate activity.
The patrols will operate in the channel between Mozambique and Madagascar.
A recent study by Geopolicity - which specialises in economic intelligence - estimates that piracy cost the international community between $4.9bn (£2.9bn) and $8.3bn last year.
In the same year, Somali pirates carried out more than 200 attacks, including 68 successful hijackings and receiving $50m paid out in ransoms, according to unofficial figures - making it the most active year yet.