Mosop, 25, clocked 1hr 26minutes 47.4sec for the rarely contested event. Along the way he broke the record for 25,000 meters run on the track with a time of 1hr 12min 25.4sec.
Both previous records had been set by Japan's Toshihiko Seko in Christchurch on March 22, 1981.
Seko clocked 1:13:55.8 for the 25,000m and 1:29:18.8 for the 30,000m.
"We started conservatively but by 15 kilometers I felt comfortable, so I pushed the pace, and then really enjoyed the race," Mosop said.
The race was part of special Distance Night festivities on the eve of the main Prefontaine meeting, which is the fourth stop in the prestigious Diamond League series.
Eight men lined up for the daunting 75-lap contest.
Mosop, the 2005 world championships bronze medallist in the 10,000m, had lapped all the other runners with 16 laps to go.
The small but enthusiastic crowd, enjoying late summer evening sunshine at Eugene's Hayward Field, gave Mosop plenty of encouragement as he completed his final lap, thrusting his arms skyward after breaking the tape.
He admitted that the unusual event had its difficulties.
"Thirty kilometers on the track is very difficult for concentration," he said, but added the distance on the regular surface was "great preparation" for marathons on more varied terrain.
"Speed training," he said.