BEIJING—North Korea has accelerated a little-known program to use its abundant coal supply to produce synthetic gas, helping the isolated nation reduce its dependence on foreign oil and withstand sanctions aimed at curbing its nuclear program.

Pyongyang is relying on coal gasification to buttress its economy against United Nations curbs on its petroleum imports, according to foreign officials and experts. It has ramped up its use of the technology in recent years, installing it in some of its biggest fertilizer, steel and...