South Korea’s terms of trade significantly improved last year as import prices fell 18-point-three percent amid low oil costs.

The Bank of Korea said on Monday that the average terms-of-trade index for goods came to 99-point-97 in 2015, up eleven-point-two percent from a year ago.

That’s the largest annual growth since 1988 when the central bank started compiling related data.

Last year’s average figure also marks the highest since 2010. The index for December reached 100-point-83, up eight percent year-on-year.

The net terms-of-trade index for products measures the amount of import goods a country can purchase per each unit of its export goods.

The index sets the 2010 figure as the benchmark 100.