Global over-the-counter (OTC) derivatives markets saw a surge in market activity during the first half of 2018, according to data published Wednesday from the Bank for International Settlements.

The notional value of outstanding OTC derivatives increased in the first half of the year to US$595 trillion from US$532 trillion. The increase was driven largely by U.S. dollar interest rate contracts, which rose to US$193 trillion in the first half rose from $157 trillion. “This increased activity may reflect changing expectations about the path of future U.S. dollar interest rates during the period,” the BIS says in a news release.

OTC foreign exchange markets also saw notional amounts rise to a record high of US$96 trillion by mid-2018, up from US$87 trillion. However, notional amounts of credit default swaps (CDS) continued to decline, it says.

At the same time, the gross market value of OTC derivatives continued to decline in the first half, the BIS reports. Gross market value declined to about US$10 trillion in mid-2018 from US$11 trillion at the end of 2017.

“The continuing decline in gross market values reflected in part ongoing structural changes in OTC derivatives markets. These changes include central clearing and greater possibilities for trade compression — that is, the elimination of economically redundant derivatives positions,” the BIS says.

The share of outstanding OTC derivatives that cleared through central counterparties (CCPs) in the first half came in at around 76% for interest rate derivatives, and 54% for CDS, the BIS says. The highest share of central clearing was for Canadian dollar contracts at 89%.