The DM139 began as a Reynard 2KQ-LM chassis that underwent heavy modification to meet the 2004 LMP1 rules. Team Nasamax replaced the original and reportedly unreliable CART Cosworth XDE V8 with a 5.0-litre V10 Judd GV5, developed with input from both Judd and the team. New regulations limiting rear wing configurations significantly reduced aerodynamic efficiency; designer Kireon Salter estimated the overall downforce fell by as much as 25 percent compared to the previous specification. Without access to a wind tunnel model, the team experimented with several rear wing designs to try to recover rear downforce.
The car ran on biofuel, which factored into several of its regulatory allowances during competition and was central to its significance as a pioneering entry.
The DM139 competed in a single full season of racing, the 2004 Le Mans Endurance Series. Drivers Robbie Stirling and Werner Lupberger shared the car for most events, with Kevin McGarrity joining for the Le Mans round.
At the season opener at Monza, Stirling and Lupberger qualified ninth and recorded the fastest straight-line speed of the session at 318 km/h (198 mph). They finished eighth in LMP1 and eighth overall, 15 laps down on the class leaders.
For the 24 Hours of Le Mans, the ACO permitted an increased fuel tank capacity of 120 litres in recognition of the biofuel's different energy density. The team qualified 14th with a lap time of 3:42.429. During the race the car suffered an engine misfire but continued to circulate, ultimately finishing 17th overall and seventh in LMP1 — making the DM139 the first prototype powered by an alternative fuel to complete the full 24-hour distance. The achievement was noted in an issue of the British science magazine New Scientist.
The team skipped the Nurburgring round. For Silverstone, Romain Dumas replaced McGarrity after an initial test session at Paul Ricard; the trio qualified tenth and ran without reliability issues to finish fifth, the car's best result of the season.
At the final round at Spa-Francorchamps, an accident during the warm-up session damaged the right front corner, requiring replacement parts. No underlying mechanical damage was found. The car qualified ninth with a time of 2:09.942 but retired from the race approximately three hours in after an accident at the corner known as Speaker's Corner. This was the last competitive outing for the DM139.
Team Nasamax submitted an entry for the 2005 24 Hours of Le Mans but withdrew before the event due to financial difficulties, bringing the car's competitive career to a close.