Both car companies have their headquarters in Bavaria, the largest of Germany's 16 states.
Research by Automobilwoche shows that of the 26 cars currently being used by the Bavarian government, 17 are Audis and nine are BMWs.
Breaking the numbers down even further, seven Bavarian ministers, including Commerce Secretary Otto Wiesheu and Attorney General Beate Merk, are chauffered around in Audi A8s. Only four lawmakers are driven in BMW 7 series.
Audi, which is a subsidiary of Volkswagen, also supplies the three business cars used by Bavarian parliament.
The president of the Bavarian parliament, Alois Glueck, "is an absolute Audi fan," said a spokesman.
Eugen Turi, office manager for Labor Secretary Christa Stewens, said, "Our drivers believe that the A8 is safer and the all-wheel drive is fantastic in winter."
BMW is fighting back by appealing to the lawmakers' sense of regional pride. Government insiders have told Automobilwoche that BMW recently sent letters to high-ranking politicians to point out the importance of the BMW to the state's economy.
Labor Secretary Stewens received one of the letters. In it the politician is reminded that "the 7 series is built in Bavaria." The letter asked Stewens to take this into consideration when acquiring a business car in the future.
Richard Gaul, who is responsible for political subjects at BMW, explained that such letters to Bavarian lawmakers are common practice.
He said that politicians need to consider that the Audi A8 is built in Neckarsulm, which secures jobs in the state Baden-Wuerttemberg, while the 7 series is manufactured in the Bavarian city of Dingolfing.
It remains to be seen whether the letters will have any impact on Bavarian Prime Minister Edmund Stoiber's upcoming car-purchasing decision. The self-confessed 7 series driver will soon test a long version of an armored A8.
BMW loses to Audi when it comes to Bavaria's politicians, but it soundly beats its rival when it comes to overall sales in the state. Last year BMW had 91,406 new registrations according to data from the German Federal Motor Vehicle Registration Agency, Audi managed only 59,466.