Coal was the company's second biggest contributor to BHP's underlying earnings after iron ore at $3.4 billion for FY2019. 

However, this figure was lower than the earnings before interest and tax result for FY2018 of $3.6 billion.

Queensland Coal unit costs increased 2% to US$69 per tonne mainly due to wet weather impacts and higher strip ratios, diesel prices and contractor stripping costs, which were partially offset by favourable exchange rate movements.

Unit costs in the 2020 financial year are expected to be between $67/t and $74/t based on an exchange rate of AUD/USD70c as a result of increased wash plant maintenance and local inflationary pressures.

"In the medium term, we expect to lower our unit costs to between US$54 and US$61 per tonne reflecting higher volumes, lower strip ratios, optimised maintenance strategies and efficiency improvements from the transformation programs," the company said.

NSW Energy Corporation unit costs increased 10% to $50/t as a result of higher strip ratios and contractor stripping costs, and unfavourable inventory movements.

This was partially offset by the impact of favourable exchange rate movements.

Unit costs in the 2020 financial year are expected to be between $55 and $61/t reflecting increased stripping costs and lower volumes as BHP continues to progress through the monocline, increase development stripping and focus on higher quality products.

In the medium term, unit costs are expected to be between $46/t and $50/t, reflecting ongoing progression through the monocline and a focus on higher quality products.