By Tetsushi Kajimoto

TOKYO Japan logged in September its largest current account surplus in 18 months as the trade balance swung into the black, the Ministry of Finance (MOF) said on Thursday, with hefty gains from overseas investments boosting the balance of payments.

Japan's current account surplus stood at 2.72 trillion yen ($18.03 billion) in September, the MOF data showed, a little shy of economists' median forecast for a surplus of 3.0 trillion yen in a Reuters poll.

It was the eighth straight month of surplus, the MOF data showed.

Japan's current account has recently highlighted the pain that high energy costs and a weak yen have inflicted on the world's third-biggest economy, which relies heavily on imports of fuel and raw materials.

Japan's position as an export powerhouse has also waned in recent years, in part because companies have moved production overseas, in a gradual shift towards making overseas investment a pillar of the country's earning power.

A breakdown of the current account data showed the primary income surplus from Japan's direct investment and portfolio investment came to roughly 3 trillion yen in September, overwhelming a trade surplus of 341 billion yen.

For the first half of this fiscal year, Japan logged a record current account surplus of 12.7 trillion yen, with primary income gains at around 18.4 trillion yen, also a record and more than offsetting a trade deficit of 1.4 trillion yen.

($1 = 150.8800 yen)

(Reporting by Tetsushi Kajimoto. Editing by Sam Holmes)