JP Morgan Chase is expected to add Bahrain, Kuwait, Qatar, Saudi Arabia and the United Arab Emirates to the emerging markets index, which already includes Oman, before the end of the summer but could still decide not to proceed with the addition, bond-fund managers said. The proposed change would fundamentally transform the emerging-market asset class, increasing its size by about 12% and adding the Gulf Cooperation Council, or GCC. These steps by JP Morgan led to an unprecedented increase in foreign investors purchasing Gulf bonds. This contributed to the rise of the bonds’ prices and the drop of borrowing cost of GCC countries. The yield of Saudi Arabia’s bond due in 2047 fell half a percentage point this month to 4.85%, reflecting an implied 9% decline in the country’s borrowing costs, according to data from IHS Markit. Yields of comparable Bahraini bonds fell to 9.1% from 10% over the same period. GCC bonds account for about 15% of all emerging-market bonds outstanding but only 10% of the new bonds issued to investors. Governments in the region have issued $114 billion of bonds since the start of 2016, about 10 times the amount borrowed from 2013 to 2015, and total GCC sovereign bonds now amount to about $195 billion, according to data from Dealogic. The entire GCC should be added because bonds from the region now comprise 14% of all emerging-market debt. “There’s a scramble going on for GCC bonds,” said Yacov Arnopolin, co-manager of a $2 billion emerging-market bond fund for Pacific Investment Management Co. that tracks a JPMorgan index. “It’s a fairly meaningful change to the benchmark.” Inclusion in the index would raise the profile of GCC countries among asset managers tracking the JP Morgan indexes, who manage about $250 billion, Arnopolin said.