Mullins has to drift his vehicle along with Schwartz so that the latter's auto can be refuelled mid-drift, from the extra gasoline tank mounted in the car's trunk.
Guinness has yet to certify the record - set by Johan Schwartz on a small, circular track at BMW's Performance Center in Greer, South Carolina - but an adjudicator was on-hand to confirm the achievement.
BMW found the main obstacle for gaining back its previous drift record set in 2013 - and summarily usurped by Toyota twice - was that the M5 kept running out of fuel, so the quirky solution was to refuel mid-drift.
Schwartz shattered the previous record by 143 miles.
Not content with setting one record, BMW set another on the same day, this one for the longest twin vehicle drift (water assisted): 63.16km.
BMW has drifted into the record books.
You'd probably want to stop for a break after driving eight hours on the highway, never mind while going in circles in a constant tire-squealing skid, but that wasn't an option for Schwartz, so the German automaker rigged up a way to refuel the M5 mid-drift with another vehicle.
"We knew going-in that if we were going to recapture the world record for longest sustained drift and set the bar as high as possible, we would need to find a way to keep the M5 going without stopping to refuel", said Schwartz.
BMW had to develop a complex refuelling system with an exterior nozzle to facilitate refuelling on the go so that the M5 never had to stop for fuel. "It was a big win all around".
The first and most important of the two records is for the longest vehicle drift in 8 hours (232.5 miles or 374.1 kilometers). As Mullins matched Schwartz's drift, Detroit Speed's Matt Butts, who was suspended via a safety tether from the second vehicle's rear window, was able to straddle the space between both moving vehicles and successfully complete the fueling.