Yancoal said in its annual report that it was actively considering the effect that its supply level could have on specific coal markets and would respond appropriately to prevailing market conditions.

"Australia is expected to retain a market share of around 26% of the growing world seaborne thermal coal requirement and to play a critical role as a primary source of premium grade coals," it said.

"To counter the anticipated short-term volatility in thermal coal price indices, we continue to optimise the product quality and volume we place into the market."

Yancoal's saleable coal production, excluding Middlemount, was up 8% from 32.9 million tonnes in 2018 to 35.6Mt in 2019 and including Middlemount was up 6% from 34.8Mt in 2018 to 36.9Mt in 2019.

This included an increase in the three tier-one assets of Moolarben, Mount Thorley Warkworth and HVO of 7% from 29.8Mt in 2018 to 32Mt in 2019.

The saleable production contribution of the company's tier-one assets increased from 86% in 2018 to 87% in 2019.

Thermal coal saleable production increased 11% from 27.3Mt in 2018 to 30.2Mt in 2019 and metallurgical coal saleable production decreased by 11% from 7.5Mt in 2018 to 6.7Mt in 2019.

Thermal coal represented 82% of total saleable coal production in 2019 a small increase from 78% in 2018.

A pre-feasibility study for an underground mine at the Mt Thorley Warkworth complex is due to be submitted to the company's board for review by mid-2020.

"At Mount Thorley Warkworth, Yancoal in its capacity as the operator, has identified a coal resource that could support an underground operation," Yancoal said.

"The initial concept study shows a potential production output of 6 million tonnes per annum of run-of-mine coal."