The nation's customs-cleared trade surplus plunged by 79.7 percent in August to 116.3 billion yen on a year-on-year basis, as the imports bill ballooned to record levels amid an ongoing runup in oil prices, the Finance Ministry said Thursday.

Imports in the month expanded by 21.1 percent to 5.1 trillion, yen marking an 18th straight monthly rise, with crude oil imports surging 49.2 percent in value terms, the ministry said in a preliminary report.

Crude oil prices in August on a customs-cleared basis stood at $55.5 per barrel, up 47.2 percent from a year earlier, according to the ministry.