As the Islamic banking industry moves from a niche sector to the mainstream of global finance, the dearth of religious scholars with sufficient expertise to sign off on “Islamic” products and the lack of standard opinions are emerging as key bottlenecks.

The range of Islamic scholars who have expert knowledge of finance ranges from 50 to 260, depending on estimates. But most experts agree that a few dozen scholars essentially control the industry, sitting on many of the so-called Shariah boards, the bodies that banks and other institutions either employ internally or hire to judge whether products are interest-free and therefore comply with Islamic law.