SEOUL, June 26 (Xinhua) -- South Korea's terms of trade worsened last month on expensive crude oil, central bank data showed Tuesday.

The net terms-of-trade index for goods shrank 5.3 percent in May from a year earlier, after sliding 5 percent in the previous month, according to the Bank of Korea (BOK).

It was the biggest fall since April 2012. The index measures the amount of imports that can be made with proceeds of a unit export.

Import prices moved up on expensive crude oil. Global oil pries surged 46.7 percent in May from a year ago.

The import value index jumped 13.5 percent on higher crude oil price, while the import volume index gained 2.7 percent.

In terms of volume, exports advanced 13.8 percent due mainly to robust demand for locally-made semiconductors. The export value index jumped 19.1 percent on higher oil product prices.