BERLIN - German automotive companies continue to dominate the global market for luxury vehicles, a study published on Thursday by the Bergisch-Gladbach technical college finds.

According to the study, the up-market brands Mercedes-Benz, BMW, Audi and Porsche all managed to achieve further sales increases during the first six months of 2018 compared to the same period last year. As a consequence, the four carmakers achieved a combined international market share of 80 percent in the sector.

In the first half of 2018, Mercedes-Benz achieved the highest number of sales of the luxury carmakers considered in the study. The Stuttgart-based company defended its leadership over Audi and BMW by selling a total of 1.19 million vehicles to customers across the world (plus 3.9 percent). Strong growth in China (plus 16 percent) hereby compensated for a slightly weaker performance in Europe and the U.S. compared to 2017.

The sales of second-ranked BMW grew by 2 percent during the same period to 1.06 million vehicles. Unlike Mercedes-Benz, the Munich-based company witnessed simultaneous growth in its Chinese, European and U.S. customers markets between January and June.

Ingolstadt-based Audi achieved the largest annualized increase in half-year sales by 4.5 percent to a total of 950,000. However, the positive development of sales at the Volkswagen Group subsidiary mainly reflected the normalization of its Chinese business in the wake of a conflict with local distributers which significantly undermined corporate performance in 2017.

Porsche, another member of the Volkswagen Group, sold 131,000 luxury vehicles in the first six months of 2018. The figure marked an annual increase in global sales of three percent.

Stefan Bratzel, automotive expert at the Bergisch-Glabach technical college, highlighted on Thursday that the companies assessed in the study gained most of their edge over competitors by placing an emphasis on innovation. Nevertheless, swelling trade conflicts meant that Germany's luxury carmakers were likely to face a tougher commercial environment in the years to come.

Due to the highly-globalized supply chains of the automotive producers, companies in the industry are particularly vulnerable to the erection of new tariff- and non-tariff barriers. According to Bratzel, the protectionist tendencies of U.S. president Donald Trump as well as the United Kingdom's decision to leave the European Union (EU) were consequently both developments which posed serious threats to current levels of profitability at Mercedes-Benz, BMW, Audi and Porsche.