This helped the company achieve a 13% increase in RoM production to 4Mt.
Whitehaven said Maules Creek's mining licence allows 13Mt per calendar year RoM production.
"After a strong nine-month RoM production performance, the maximum RoM production permitted for the December quarter is 2.6Mt," the company said.
"However, with healthy levels of coal stocks, sales during the December quarter will continue to be strong."
September quarter saleable coal production of 2.4Mt was 11% above previous corresponding period, reflecting the RoM production profile, partially offset by lower yield.
The decrease in yield reflects the mining of lower yielding coal seams located near pit-bottom, per the mine schedule.
Sales volumes for the quarter of 2.5Mt were slightly above previous corresponding period, despite a number of September shipments slipping into October due to vessel queuing at Port Waratah Coal Services.
Equity metallurgical sales of semi-soft coking coal for the September quarter were 0.3Mt, representing 13% of sales volume.
Coal stocks for the end of the period were 1.9Mt, reflecting strong RoM production over recent months and improving RoM coal feed performance at the coal handling and preparation plant.
Whitehaven CEO Paul Flynn said thermal coal prices have reached record highs which will be reflected in significant cash generation over the coming months.
"We continue to pay down our senior debt facility; we expect to fully repay the debt facility early in CY22 and be in a net cash position in the March 2022 quarter," he said.
"After a challenging period at Narrabri, we are readying for the longwall changeout ahead of a more productive second half.
"On September 16, we received Federal approval for our Vickery Extension Project, the culmination of an exhaustive process of technical evaluation and stakeholder consultation spanning five years. While we maintain our cautious approach to capital allocation, this is a critical milestone in our development pipeline that offers us optionality."