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Oil and Natural Gas Properties
 9 Months Ended
Jun. 30, 2021
Extractive Industries [Abstract]  
Oil and Natural Gas Properties Oil and Natural Gas Properties
Oil and natural gas properties are summarized below:
June 30,
2021		September 30,
2020
(In thousands)
Proved$373,367 $326,420 
Unproved22,294 32,084 
Work-in-progress15,008 15,398 
410,669 373,902 
Accumulated depletion and amortization(81,787)(63,176)
Total oil and natural gas properties, net$328,882 $310,726 
Depletion and amortization expense for proved oil and natural gas properties was $6.7 million and $4.8 million, respectively, for the three months ended June 30, 2021 and 2020. Depletion and amortization expense for proved oil and natural gas properties was $18.7 million and $15.5 million, respectively, for the nine months ended June 30, 2021 and 2020.
The following table summarizes the components of exploration expenses:

Three Months Ended June 30,Nine Months Ended June 30,
2021202020212020
(In thousands)
Expiration of oil and natural gas leases$2,785 $6,757 $8,615 $7,288 
Geological and geophysical costs— — 67 1,943 
Total exploration costs$2,785 $6,757 $8,682 $9,231