The company's supply of thermal coal to the Australian domestic market plunged 23%.
Australian coking coal production of 4.3Mt for the half year was 900,000t higher than H1 2018.
The decision was to maintain Glencore's attributable global coal production to about 150Mt.
Australian coking coal production of 7.5Mt was 23% higher than in 2017.
The calmer industrial environment in 2018 allowed Glencore to increase its production.