Four adult pals in Oklahoma who went off on an evening bike ride together on Sunday night haven’t been heard from since, police said. The four friends—Mark Chastain, 32; Billy Chastain, 30; Mike Sparks, 32; and Alex Stevens, 29—set off in Okmulgee around 8 p.m. Sunday. Their families reported them missing on Monday evening, after all calls to their phones went directly to voicemail. Police have yet confirm a report that the friends were spotted walking together at 2 a.m. on Tuesday. “This evening and tomorrow we will begin the long and tedious process of sifting through the hours of video as well as the GPS data,” police said in an update on Facebook. So far, police said there’s been no indication their disappearance involves foul play. “They don’t go far—never,” Mark Chastain’s wife told a local news station.