Corporate oversight of so-called conflict minerals is waning amid a relaxed regulatory environment, according to an Oct. 18 report from the Responsible Sourcing Network.

Intel Corp., Microsoft Corp., and Apple Inc. continue to lead the network’s annual ranking for their work to investigate and mitigate minerals-related risks in their supply chains. But for most of the roughly 200 companies sampled, their scores stayed flat or fell this year.

The report’s author Raphaël Deberdt blames the general lack of improvement on the Securities and Exchange Commission’s recently relaxed stance toward enforcing its reporting requirement on conflict minerals, now in...